In my early 20s, once I got back into console gaming with the original Xbox, I'd buy basically every game that caught my eye. Many/most of them I never played to completion. I was really only capable of focusing on one game at a time, and I'd spend little-to-no time on my backlog because something shiny and new would always be coming out.
I changed those bad habits to a certain extent with the next generation. I wouldn't allow myself to have a backlog (well, outside of the floodgates opening around my birthday/Christmas). I made it a point to get to the end of most (but not all) of the games I played.
But it really wasn't until my mid-to-late 30s where I started to be die-hard about it. With the exception of ZombiU, I went back and finished every game that gen that I'd started and hadn't finished. I started chasing achievements and trophies. I don't feel some psychological compulsion to platinum or 1000/1000 my games, but if it's feasible/enjoyable for me, I'll do my best. Open world games prey on my weakness, so I almost always 100% them. Maybe I won't get all the achievements, but if there's an upgrade I can get or an icon I can clear off the map, I'll do it.
So, yeah, I'm far more likely to 100% a game at 41 :p than I was, say, 20 years ago. Heck, or even 10 years ago.