I'm 44, my daughter is 17 and roughly two years away from leaving the house. I've picked up more physical activity again and plan to do dive into regular intensive yoga next year. Also as a long term investment in my health and old age.
Sex is better than ever, allthough I've finally had a pleasant share of affairs in the last few years and thus don't feel like I'm missing out all the time anymore - which takes away quite some pressure and is a great thing too. I've also grown man enough not to take any crap from woman anymore whilst at the same time treating them with respect and fairness. I picked up tango dancing 7 years back and since have gained a bunch of lady-friends that are smart, intelligent, breathtakingly beautiful and of the type I wouldn't have dreamt of even talking to 15 years ago.
I've gained in self-respect and in respect for others and I've made a point of systematically and continously improving my social skills. Wore a tie for the first time in my life 2 weeks back. Gray hair == shirt & tie person with decision authority. Neat. I've gained solid experience for the job (web-centric FOSS web development), smell bad projects from miles away and know how to treat marketing, customers and collegues so as to get along with them.
It's the nerd advantage all over, if you take good care of yourself. Which I strongly recommend. And don't wait to long for having children. 27 seemed to early for me back then and I was scared shitless, but I'm so glad it happend so early today. Later in life your former jock classmates will be all fat and wasted and you'll just be running up to full throttle.
Avoid alcohol and smoking, pick up something intelligent with excercise (Martial Art like Aikido, Kung-Fu or something, or social dancing like Swing or Argentine Tango (helps you meet the ladies too)) and see to it that you have a solid throughput of encounters with the opposite sex. Learn a musical instrument and learn to shut off the computer, go out, meet and talk to people. Learn to technically manage your habits, especially the bad ones.
Who knows, once my daughter is on her own I might even to a career switch or move to some cool city like Amsterdam, Berlin or Paris.
Stay healthy, avoid dept and to many material goods and bondings like the plague and be ready to learn and change your vantage point on life once in a while. Do all that and aside from some wrinkles, gray hair and a constant increasing pool of experience and coolness you won't have any signs of aging for most of your life. Types of people of whom you never thought would be interested in you will ask your advice, crave your presence and even look up to you. It's a very awkward and suprising, and a whole new experience - but an ultimately rewarding one. Don't miss out on that.
Good luck in your life.