i need your opinion!!!

Okay so i need your guys opinion!! Befor my grandpa and great grandpa died i told them i was gonna join the navy...But the thing is my mum is totally against it she said if i wanna join in kind of thing like that she said the airforce...But then my dad wants me to do what i want....{I kno i still have like technaclly 4 years tili can join but still} i dont kno what to do... Any advice or anything?!