I don’t believe in drawing an arbitrary line for any part of transition. So I would never say an age is “too young” for anything. Perhaps a person at the age needs to wait a little, but without knowing you, I could not possibly say whether or not I thought you were ready to start testosterone.
People do start at 15 and even younger. The ones who start younger, typically do so after being on hormone blockers for a while to delay puberty, and start T so that they go through male puberty at a similar age as their cisgender male peers.
The adolescents I’ve talked to who transition around yr age usually decide to wait a couple or a few years before starting testosterone. This is sometimes their decision and sometimes enforced by their parents and/or doctors. Adolescence is a crazy time anyway, so if someonecan delay a medical transition, it sometimes is the right thing to do. Especially if you are in a community that accepts you as male.
In the UK, I know they are not allowed to give trans guys under 16 (or is it 18??) testosterone. That is not the case in the USA.
This is something that you will have to decide with yr parents and doctors. Best of luck :)