I'll side with your Dad and say, get the bigger bike you can grow into. At 13, you are on the cusp of another growth spurt. You will dwarf an 80cc bike and be bored with it in a year.
im 13 and i want a dirtbike but i dont know what cc would be best. my brother says 80 but my dad says 100 or 125. i have a 90cc fourwheeler and its pretty good. a little slow but good.
I'll side with your Dad and say, get the bigger bike you can grow into. At 13, you are on the cusp of another growth spurt. You will dwarf an 80cc bike and be bored with it in a year.