How many miles should your first car have on it for it to be reliable?

im turning 16 in 6 months and have been looking around for cars. i really like the scion tc but all the ones i have come across in my parents/my price range either have like 80-90k miles on them or are stick shift. what is the limit for the amount of miles a teens car should have so it will last them until after college? and i dont think i want a stick shift... any thoughts?