how old do i have to be to get my scuba diving license.

In the USA, the major recreational scuba training agencies allow children 10-14 to obtain a Junior certifications. The standards vary some between the agencies, but in general the Junior diver is permitted to dive with restrictions under the direct supervision of a certified adult. A Junior certification can be upgraded to an "adult" certification once the child reaches the age of 15.

Whether this is a good idea or not is a whole different discussion. There are physical and psychological reasons that suggest it may be wiser to wait until the child is older before exposing them to the hazards associated with diving.

By the way…it is a certification, not a license. In most areas of the world, scuba diving is regulated by the scuba industry not by the government