Tough to tell. I have a former eye surgeon who is 78 and has progressed to 3 pull-ups, good DL form w/115lbsx10 and an assortment of other accomplishments.
He has always eaten kinda low carb and gravitated to the paleo stuff easily.
I have folks in their 50's who are far off his fitness...it's just a crap shoot.
"Survival will be neither to the strongest of the species, nor to the most intelligent, but to those most adaptable to change."