I'm 43 and started boxing 2 years ago. I'm too old to compete but I train and spar at the same level as the younger boxers in the gym. My fitness isn't at the same level as 25 years ago but as long as I keep the same workrate as the younger boxers I'll continue with the sweet science.
My only advice to you is to train at the same intensity as the younger boxers in your gym and don't rush or be pressured into a fight.