I'll be 40 in December, and I don't feel any decline in gym workouts. I believe strength is the last thing to leave an athlete.
I do think I can hit a 365 bench this year at 175...IF the gyms f*cking open here.
My only concern is I feel I am somewhat more prone to injury, and will need more time warming up, to hit my max lifts.
I also feel that I require slightly more time to recover.
As oldtimer1 said, I think 40 may well be a gym rat's prime.