When your nasal and ear hair grows faster than you head hair.
When you find yourself in a revolving conversation with a pimply faced kid about the bike in the back of your ute that goes something like this.
"G'day mister what kind of bikes that?"
"It's a bultaco son"
"Oh cool, what's that then a Honda, Suzuki, Yamaha?"
"No it's a Bultaco"
"Sure but who makes it Kawasaki?"
And around we go.
When you call a 20 y/o a "pimply faced kid"