Maybe 25 in my case, I started when I was about 12 on a Mac Plus, I'm 37 now. Contributed to some small indie games and half-finished a few dozen, but decided to give it up because there is just no money in it (as a whole I mean, I realize a few rare winners make it above the fold though).
I would say it's at least 10 times harder to make games than normal applications, but, programming networked apps is at least 10 times harder than making games. This probably includes startup apps that that use the newest languages and databases.
I've generally found some of the "harder" concepts like 3D to actually be pretty easy, because so much effort has been thrown at them over years. It turns out to be a lot harder to interact with the OS since it's a moving target. For example, pretty much the entirety of what I wrote before about 2010 is unusable for Mac or iOS programming today.
To really make money, it’s critical to write as little code as possible (preferably no code at all), or be willing to let your games slip into obsolescence. Nobody ever talks about the amount of work it would take to bring a game from iOS 4 to iOS 8, or that most games make $1 a day or less. It’s pretty grim. So, best not to think about that stuff, and just concentrate on making something somebody might appreciate that has the potential to go viral. Or, do it as a hobby, don’t waste a decade or two trying to make it a career (unless you work for an established company, because sequels take the least amount of creativity and make the most amount of money - like Birdman for gaming).