Because crossover fanfiction aficionados enjoy having characters played by the same actor be secretly the same people (or at least related)? And this is Marvel Universe, where science, magic, or some freaking amalgamation of the two can explain drastic changes in people? (Max received a variant of the supersoldier serum! Kevin was a mutant, whose mutation killed him but allowed him to pass on his intelligence to his best friend! Max was secretly partly alien, which means that his maturation was completely different and he secretly wasn't stupid, just ugly duckling-y! Once he finished his physical growth, his mental growth began!)

Also, the loyalty both characters show towards those who are physically disabled and therefore isolated from those around them indicate a somewhat similar personality and bent, which could well belong to the same person at different stages in his life. Also also, I've had fun with end punctuation in this post. Please don't judge.