Some people believe that by comparing one's age to their PROVEN growth pattern, you can estimate where and when they will peak.
For example, if a guy goes from a 70 to a 72 in a given rating, and is 22 years old, you can reasonably assume that in five more years, he will end up around 80+/-2 in that rating, given a consistent coaching level. NOBODY except DITR have ratings growth spurts.