I was still playing games a bit in my mid 20's (this was in 2010) and only had a PS3 the year before, so was going through the likes of Uncharted which I missed out on previously. Also had my Wii going as well and had the likes of Brawl, Mario Kart, Mario Galaxy and Punch out on there.
My dip has mainly been in the last few years, though this was mainly due to work issues at the time. Yakuza 0 got me out of that slump but I haven't been arsed to play much more recently. Once the football season finishes though, that might change.
You could argue that when you start to hit mid 20's, you're focusing far more on a relationship, career, family, social life etc than playing some games.
As for gaming becoming difficult for casual players, I disagree entirely. Many games these days are 'easy to play but difficult to master' due to the games depth. The likes of Street Fighter and possibly FIFA to a small degree fall into that. Simply put, if you gave a casual player a game from the NES era, they'd be fucked before getting fucked.
I agree that more choice these days is always better. Unfortunately, you get the likes of EA and Activision that are more interested in bleeding you dry than creating a good game. Thankfully, that's where the Indies come in as they can cater to a broader audience whereas most casuals would usually play your 'AAA' titles only.
As for MK11, I would be tempted but you know the super duper edition with everything in it will be out in a year and for much cheaper.