Based on what I know about myself relative to AP in HS, and about sprinters and footballers in general, AP could have been a clean low 10.3x 100m guy at his peak, had he specialized in sprints (although it is very hard to say, because it is unknown what his body mass would be if optimized for sprinting--he may well have been a clean 10.2x 100m sprinter).
On the PED that is now in vogue, he could possibly have gone low 10.0x or maybe even high 9.9x. That is my sincere appraisal of his ability, should he have cared to specialize, and to use.
He's a damn fine athlete--obviously. Right now, he would be lucky to run 10.9--too banged-up, WAY too heavy, and force is applied for too long to have required turnover to go any faster.
He is an NFL RB, not a sprinter--but he could have been a damn fine sprinter, even national-class, IMO. I have seen some NFL guys his size with excellent sprint talent, who went around 10.90 FAT during serious football activity. They do too many weights and not enough top-speed running to do the 100m any faster. They are carrying around too much body mass (his Wiki page lists him at 6'1", 217 lbs), and especially RB's and FB's learn to apply force to the ground for too long--great for football, not great for sprinting.
These guys can have pretty good 60m times, though, even around 6.8x or 6.9x