My mum doesn't support the fact that I want to join the SAS?

i am 15 and i really wanna join the air force too... i talked to people that has been in the air force and stuff around... most of them said the first few years is the hardest and that there is a high chance of dying.... my grandad was a very high rank in the air force before he retired... but dont you have to be like 18 unless you are joining the specail forces.. for 14-17 ect...