Mental engagement in particular
Somewhat. It has to do with memory, though; the brain is not a muscle, and working it does not keep it healthy. Each time you remember something, however, it does become more linked and thus more accessible; this is exactly as true at age 8 as at age 80, barring dementia or other mental disease related to the structure of the brain failing.
The funny thing is mental exercise doesn't strengthen the brain. The brain is not a muscle; it doesn't become stronger with use.
People think I'm a genius. It took me forever to realize, of course, they're right. Of course I'm a genius. It all makes sense. I didn't put my brain on some kind of mind-treadmill to get this way; it just is.
Being a genius is all about technique. The brains of great memorizers like Dominic O'Brien or Ben Pridmore are exactly like the brains of the average human. The brains of genius thinkers are similarly a near-match for your average flaming dumbass. It's all technique.
Each time you interact with a piece of information, it becomes more fixed in your mind: the more you use English or Japanese, the better you get with assembling or interpreting sentences in those languages, even though you won't get better at other languages that way. When you study a new language, you steadily pick up habits conducive to learning new languages, internally and externally. When you study math, the mathematical formula become entrenched in your mind; new formula work on the same concepts, and thus are readily understood.
Mnemonics are a good place to start: with immediate access to piles of information comes immediate association with new information and new problems. Just as with math or a language, you strengthen your mind's grasp on mnemonic techniques each time you use them. Just as with developing habits to learn languages, you can develop mnemonic techniques like Method of Loci and Major System, or habitual study methods like SQ3R. Like any new habit--driving, a new sport, Go or the inferior Chess, novel writing--it will be exhausting at first, consuming analytic resources and activating the energy-hungry prefrontal cortex; with use, the habit is encoded in the energy-light basal ganglia, and becomes natural and easy.
By encoding these behaviors into your study habits, you train yourself to take in, make meaningful, categorize, organize, store, recall, and put to use new information rapidly and efficiently. The immense and exhausting effort of learning new things still happens, but it happens for a much shorter time, and at much reduced load. Because you remember more of what you're learning, it becomes more meaningful: whatever you just learned in the previous section is memorized more completely, and can be recalled to explain and give meaning to what you're learning in the current section, thus making both more memorable and strengthening their encoding in your brain.
The ability to quickly learn new things makes you smart, unlike normal, dumb people who can't learn shit. The ability to quickly recall what you know as related to what you want to accomplish is the ability to quickly solve problems, which also makes you smart. Apply your knowledge effectively and you stand out from all others. You can even compare IQ tests with every abstract and logical problem you've ever seen, applying familiar reasoning to familiar problems, and familiar analysis to unfamiliar problems, scoring higher on these tests than you otherwise would--and then you can pass a MENSA exam, and have a framed placard stating you're a certified genius.
Memory capacity, and all implied by it, don't decrease with age. Consider that as a final point: bluntly playing the same mind games (e.g. sudoku) won't keep you smart; but your brain won't decay unless taken by serious disease.
or goes to bed too late?
The implication is that humans are genetically predisposed to be awake for a few hours after the sun goes down, and sensitive to daylight. It's the same as tulips opening at night, or mice sleeping during the day. It appears 80% of humans are genetically predisposed to stay up later and wake up later than agrarian society dictates (you have to get up way early to tend crops and milk cows).
It's been happening forever. In the 1500s, a Catholic Priest dedicated his efforts to attacking the mnemonics techniques used to memorize scripture--and everything else--because they attached lewd and base images to ideas in the mind. This happened after one preacher admitted he used an image of a naked virgin girl in a not-so-puritan situation to help remember some odd line of the Catholic bible. Having such thoughts in peoples's heads was unacceptable, entirely.
I've noticed about five people have responded, and some of them have user IDs in the millions. That's a pretty small cross-section; and I've had up to 50 responses to posts on Slashdot in under an hour, when I've really pissed the crowd off with some uncomfortable fact. I'm not taking much stock in the overwhelming rise of the majority rule of morning people here.
There is some evidence that 80% of the population awakens far too early, to detrimental effect on health. The idea has gained some traction slowly over the past decade or two; in the next 30-40 years, I expect we'll link circadian disruption by bastardized early-riser sleep culture to the high incidence of stupidity, depression, and psychosis leading to school shootings.
Sticking your child in front of a video game to parent for you is NOT engaging.
Children need independence. Independence doesn't mean mommy isn't around; it means they make decisions and mistakes on their own, and are able to move away from their parents and return by their own action--even if they're instructed when to do so. Such instruction is engagement, as is parents asking where you're going, where you've been, what you've done, and having food prepared for you when you get home.
We can extrapolate theoretically from here, but that's not the point. Above illustrates that parental engagement does not require your child to be chained to a desk with a single activity when not engaged by the parent. My argument was on this balance of time, and on the impact thereof in regards to independent social and environmental experience versus isolation with a single activity.
To compare: we could also talk about break time spent smoking versus break time spent walking around the building. If you bring a healthy diet into this discussion, you are babbling on about irrelevancies.
This is 2014, and we're in the decade of reboots. This is the reboot of "sit your kids in front of the TV to watch the Children's Channel" thinking. The glowing, phosphorus parent of the 80s, now back with less Big Bird.
Put your kids outside. Don't put them on the bicycle of the Internet; put them on a *real* bicycle. I walked the 1/3 mile to school when I was 6; I could bicycle 1.2 miles in that time, a good 10 minutes walking by myself, well out of sight of my parents. When I was 8, I had a bicycle with a coaster brake, and would disappear outside for hours at a time--by myself, since I had no friends. Sometimes I came back home after the older 5th graders beat the shit out of me for some Freudian satisfaction related to their small penises (too impatient for puberty I guess), I'm sure; but, for all the baseball bats and tennis shoes they applied, they never managed to put a bruise on me, so I made out alright.
This is all a bunch of wanting your kids locked in a room doing a single thing, in a place you know, with the ability to look in and verify they're still doing that one thing and nothing else, so that you don't have to show any concern. My massive internal simulator predicts, via armchair child psychology, that this will not provide a robust set of varied experiences for the child, and so will slow their mental growth and reduce their ability to thrive. History will prove me correct--has proven me correct--but I'm sure nobody will listen and, when it's all well proven that this actually happened, will instead find the next substitute single activity and claim it's different, somehow, and fail to predict the same result.
Who the hell do you know is a morning person? That one dude at the office? How many people are awake like, "Ugh, fuck, too early for this shit, coffee..."?
They say it's DSPD. You won't sleep like a normal person, you stay up late, then you don't get up until 10 or 11. Yeah, right. And normal people enforce a bed time, drag their asses out of bed groggily, then come in and futz around for a few hours until about lunch, and suddenly become active.
Guess which behavior's normal?