I feel your pain, I don't even bother with online shooters anymore, my reaction times are crazy slow these days. ARC Raiders looks a lot of fun but just no.
Hmm interesting - I'm in my (early!) 40s, don't play loads of shooters regularly, but dip in with TF2, a BF (usually 4) game or single player Doom. I find of course reaction times are glacial relative to when I was younger but muscle memory comes back fairly quick, I cut my teeth on Quake so twitch gaming is baked in solid but I recognise I tend towards being strategic in play more so than when I was young. Simply put can't rambo through a map and expect to get far. So working angles know maps, and. you can still rack up a decent score k/d ratio.
I keep being reminded of playing touch rugby as a teenager and having a few 40-50 yr old ex rugby players on the pitch and they were slow, but gooooood, they just used their experience and didn't make too many mistakes, and I see that same thing in how I play the more competitive games online now. I haven't tried an RTS in a long time competitively, and I played SC/SC2 at a fairly high level back in the day, I suspect that would be much harder to keep up with!

