Check out Ali after prison time. depends on weight class and how they fight to whether it's noticeable or negative on their performance though... I'd say after 25 you start to lose certain physical attributes... But they can be made up with experience and ring smarts which you earn during and leading up to this time.
They claim speed starts to decrease after 25 but surely this has several ancillary factors worthy of consideration.
Alot of factors man. Injuries, muscle deterioration, weight gain, inactivity in the ring, etc. Fighters that been in many grueling wars usually are first to lose them.
Just hire a known steroid distributor and take steroids like Marquez did then claim everything is clean and you won't have to worry about that
