You can game when you're a parent, just fine. Yes, things change with kids in that you've got them as an over-bearing responsibility, but that applies to all of your hobbies - it doesn't affect gaming in particular, you just have less free time. But if you're gaming so much that it's affecting your employment, well you've got other problems and probably need to seek psychological help. Again, that's no different to any other hobby - if you're spending so much time at the gym, or out for coffee, or reading recreationally, that it's affecting your job, then that's a problem too.
I've found that as I get older (mid 30s now), two things happen: (a) I have less free time, but I can still spend the same proportion of time gaming as ever. but (b) you end up focussing more on indies and smaller developers because the mass gaming trends have been simplified so greatly in the past decade that the biggest titles aren't really challenging or interesting. Try finding a turn-based squad strategy, or a real-time one with the same complexity and strategy, or a good space-trading-sim, or a tactical rpg aimed at adults - it's surprisingly tough. Given that the average age of gamers is around 30, you'd expect that there'd be much more available for us, but gaming forums and sites tend to be frequented primarily by younger gamers, mostly in their teens, and that affects the feedback developers get. I think it's just also a more reliable target market - they know from games like Minecraft that there's plenty of my generation still gaming, and that we want a bit more cerebral complexity, and aren't too worried about the graphics, but they aren't really sure how to nail it. Other times, it's just corporate cowardice - case in point being the previews for the new Deus Ex 3, following the 'streamlined' approach and smaller maps of the failed DE2 rather than the massively successful original - that's a title that has no cache among the younger generation, or the console market, but they just baulk at taking the plunge even if they know there's a solid market out there for that kind of game.
As for young kids and gaming - it depends on the game. By that, I'm not just talking the presence of adult content, but also what intellectual challenge it is providing, and whether they are developing any skills out of it. I actually think I gained quite a bit when I started gaming on my parents Apple IIe when I was 6. I needed to read the rather thick manual to learn how to use DOS (no graphical interface, or mouse, in those days - you had to learn the various load, run, directory, dir/w, save, drive change, folder change etc text commands). I played Wizardry 1 to death that year. Again, you absolutely had to read the manual in those days - it was the first rpg system that I encountered, and so I had to read and learn the concepts of levels, exp, damage, the spell lists (none of those were accessible in game, only how many spell slots you had left), what spells were better against what types of monster, and which spells cured which status effects. Obviously that's not exactly 'useful' knowledge, but it meant that I had to do a huge amount of reading, and a huge amount of maths. Also, like all crpgs then, you had to handmap the dungeon using graph paper, with the hardest part of the game being all the tricks that they threw in to make you lose your way usually resulting in death (which in Wiz 1 meant perma-death unless you levelled up another party and sent them down to retrieve the corpses) - rotating rooms, teleports (sometimes to a room that from that square looks exactly the same as the one you were teleported from), pits that dropped you down a level, mirror-rooms (moving north sends you south, etc). Again, not directly useful as lifeskills, but the problem-solving was far better as mental exercise than, say, watching TV.
It's hard to find similarly challenging games that a kid could play these days - the few that provide any degree of mental challenge tend to come wrapped in adult themes that aren't really suitable. When games consisted of white-on-black 'wire' block maps with a still-image picture representing the monster type in the group you were fighting, it didn't really matter that a kid was playing a game involving killing and fighting - you can't really have a 7 year old playing a modern crpg where you actually see the stabbing and the blood.
Your best bet would be something like Minecraft - not my cup of tea, but you'd be surprised how much more patience a bright young kid can have with that kind of game compared to a teenager. You want something that he can use creatively in the same way that he would use a lego set, rather than a game that gives him a set of instructions and tells him to press a button at the 'right' time. So that leaves out things like brawlers, arcade games or modern crpgs. He won't be ready for genuine strategy games yet, so that removes things like the Civilisation series. I'd say a puzzle game that allows for creativity and experimentation is the best way to go.
