There are no laws about what age you have to be to date, so it is legal. There are laws about sexual activity depending on the state. In most places you have to be at least 16 to consent, if not 17...
It is possible to legally marry in New York state at age 14/15. That requires parental consent and a court order. 16 and 17 require parental permission. 18 and above are on their own.