why is floyd considered past prime and wlad is considered in his prime right now when they are both the same age
Wlad is actually a year older than Mayweather. Also, bigger fighters age better than the smaller fighters. Lastly, both guys are slightly past their primes but are still excellent performers who are amongst the best in the sport.
Prime for the heavyweight is greater than the welterweight due to the greater emphasis on power over speed at heavyweight. Speed is the first to go which means younger prime for welterweights.
A fighter's prime isn't determined by age. Some fighters peak in their 20s, others in their 30s. Guys like Fernando Vargas and David Reid were shot long before they hit 30. While someone like Glen Johnson didn't really hit his peak until he was well into his 30s.
Wladimir has many more years left before he is past prime, Floyd physically will be past prime soon but I think he has the skills to fight on for a good while longer but he won't want to.