2 years younger per level. Basic analysis stuff. There is a reason where you seem to be the only one that thinks an older player doing well is a prospect and you do this all the time.
Kingery has lots of tools which sets him apart from Coppola. And Pullin is fighting some of the same stuff as Coppola being an older prospect without great tools. But Pullin also has generally been 1 year younger per level as Coppola.
Basically being Ben Revere but not as fast (Revere was stealing twice as many bases at a higher percentage success rate and getting lots of triples) is just not a good toolset to start with.