Space Ace (1984)

Dexter is the dashing Ace hero who fights against Bort and his Infanto Ray, which turns beings into infants. Alongside Ace is his girlfriend, Kimberly, who helps fight Bort and his goons when she's not being abducted. When Dexter gets hit by the ray, he turns into his gangly younger self, and has to depend on his wits to defeat Bort, while he is without strength.