If Jim Brown didn't retire at age 29 he would still own pro football rushing records....just like Wilt still owns pro basketball scoring records....and Brown only played 12 games per season for most of his career. If he'd played 16 games like they do today, he's probably have 20,000 rushing yards and 200 rushing TDs.
he would also be DEAD right now. Because in those days, they did NOT play. There were no pansy assed rules prohibiting people from hitting you in 50% of your body like there is now. There was no pussy "plain of the goal line" rule or "pilon" rule. You either got INTO the endzone or you didn't. You played 12 knock down, drag out games then you played for the championship