Is it grooming if

I know this has been asked before but I'm genuinely curious, suppose if two people A and B are 12 and 15 when they start dating and they've been dating throughout their adolescence. B will experience high school and college first and they mature faster obviously and i feel like this time period is very fast paced everything changes a lot in a short period of time.
do you think it's okay for B to continue dating A when B reaches adulthood? like when B is 19 or 20?