You have grown and your video-game tastes have changed. The old games were cool and bring you nostalgia, but they don't match your taste anymore, so they're not as fun. You need to rediscover what you like.
I've been through this (although I'm not 50), and while some of my childhood games are still super fun to play (e.g., Street Fighter Zero 2), others are just not (e.g., Streets of Rage 2). But for example, in the case of SoR2, I find there are modern variations of the game that are fun to play, like I enjoy playing TMNT: Shredder's Revenge with my kids.
I also find that different games require different "mental states" and so may not be appropriate for certain days. If I'm more in the mood for a "literature" game, I may replay Chrono Trigger or a modern RPG. If I just want to chill and get into flow state I may either just build something on Minecraft in my kids' world (if I'm tired) or play a few rounds of Cuphead. If I want to get my heart rate up I'll play some Street Fighter V online. They are all very different games. If I only have a few minutes I may play a match of Hearthstone.
Also, one thing I realized is that most AAA games do not appeal to me at all. They seem all like the same canned stuff with a slightly different taste. I also concluded that, due to the heavy Natural Selection process of the industry, if an Indie game surfaces and people say it's good, it's generally really good.
Anyway, experiment. Rediscover your taste! There's a videogame for everyone out there!