when shoukd i visit a gyno?

i’m 15 but sexually active (i have been in my relationship for 2 1/2 years and i was smart enough to talk to my mom about it and get me on birth control so don’t jump to conclusions) anyways i talked to a gyno and they said even if i’m sexually active i don’t need to make an appt unless i see that something is off but if everything is fine i should wait til i’m 21 to start making regular appointments.......that seemed kind of weird to me what do y’all think