what pisses my off is that 21 in game days ago this brat was so small he could sit on his mother's lap, now after one jacuzzi bath with the same mom his testosterone levels shot up and he straight became tall and lean captain america style.
I fully agree with your assessment. When the Parkers arrived at the San Alejo airport Dylan was (at most) 5'4" and 120 lbs. This weight was established by Sophia's thoughts when Carl took the detour through the city on the way to the suburbs. Now at the theater, Dylan is arguably 5'8" and if he maintained the same frame he would be 145 lbs.
I believe that this is a lost opportunity for an original story element. If L&P had (through time jumps) allowed four months to pass from the airport scene to the movie theater scene with Dylan enjoying this same 'Captain America' transformation he would have created a brand new game tag (the 'maturing' tag). As Sophia became more disappointed with Liam while seeing Dylan physically mature in a believable growth-spurt way, she develops amorous feelings for Dylan. This approach would have intrigued me much more than the Romper Room sex education approach.
As an aside, I agree with other commenters that have pointed out Dylan's lack of thigh and glute development. I expect a soccer player who is capable of performing 'hat tricks' would have some serious lower body strength.
Thank you for your attention, Jack.