I've been spending many hours of my free time in front of a screen like now, close to every day since the day I got my first personal computer (an IBM PC clone back in 1982).
This was two years before I landed a job working on PCs (chief responsible for all hw/sw on IBM compatible PCs in Norway's largest corporation), when I understood that they wanted to pay me good money (50% more than I was currently making) for doing what I was already doing as a hobby I was very pleased indeed.
Since then I've written several tens of MBs of code (about 20+ MB before 1990), most of it in my free time even if I later could reuse many programs & algorithms in my daytime job. I have always had at least a couple of computers at home, currently I have just one big deskside tower and a bunch of laptops. They run Windows 7 & 8, as well as FreeBSD (my gateway/fw/ntp stratum 1/ipv6 gw box) and Linux.
I've been able to work on a lot of interesting projects (if you google my name you'll find a few), including game code, ntp, crypto, graphics, video/audio decoding, simulation and modeling.
Currently my main hobby project is to take raw LiDAR point clouds and use pattern recognition to try to generate vector base maps for orienteering, including shades of green and yellow to represent various degrees of runability and visibility.
When I was ~20 years younger I won or made it to the podium in several programming/optimization contests, these days I've taken part in 3 of the 4 Facebook Hacker Cups that's been held so far. I usually make it to the second main round but I'm not fast enough any longer to get into the top 100 who make it to the finals. The main part is that it is fun to figure out problems and come up with efficient algorithms!
They key message here is that even though I'm getting closer to retirement age, I have absolutely no plans to stop thinking/thinkering!