If a 44 year old (former) athlete could make an NFL roster at a skill position today, we would be seeing at least one of them out there. You can slow down the effects of aging on maximal heart rate, VO2max, loss of muscle mass and declining recovery ability, but you cannot stop it. But that aside the idea is just silly. If Owens were to make an NFL roster today he would either be attempting a comeback after seven years of NFL inactivity (and about 14 years past his physical prime) or he would have been on an NFL roster for twenty two years at a skill position, which means he would probably have had at least three career-ending injuries by now and would be on his second set of artificial knees.