Some basic information about teen sex in the United States:

All 50 states have Romeo & Juliette laws allowing exceptions for statutory sexual assault crimes when sexual activity is between peers of similar age. The typical threshold is 5 years.

However, the floor of R&J statutes is typically 14 or 15. So a 13 year-old having sex is conspicuous. But also, teenage dating and boyfriend / girlfriend relationships often do not feature or even imply a sexual relationship. (When I was fourteen, I and a 10 year old family-friend decided we were bf/gf, even bathing together and having sleepovers, though doing nothing more risqué than Parcheesi.)

As a note, R&J laws often omit allowing for same sex intimacy. So if you're a teen exploring your LGBT+ side and want to keep it legal, check your state and county ordinances to see what is allowed.