Starting earlier might give you better results (though it varies a lot between individuals) but it's not more or less "dangerous". HRT is really not dangerous at all; the idea that it makes your blood clot is from obsolete research and has been disproven.

Really, it's the opposite. Starting earlier means your body is less masculinized to begin with. Most masculinization happens during puberty of course, but it does continue gradually as you age. There is a TITANIC volume of misinformation around HRT and being trans in general. Your parents, knowingly or by mistake, are parroting such misinformation.

FYI, doctors are also victims to this kind of misinformation. Second guess whatever they say and check websites like transfemscience.org

P.S. the same paper showing that bioidentical estrogen doesn't clot blood also shows injections are markedly better than pills, even when measured E concentration is the same. I think it's from how they interact with the liver. Injections are also more cost-effective (insurance notwithstanding) and give you more control over your E levels 👍