Could be at very small degrees though...
My dad is sixty and you could barely tell he has a tiny lack of density at the crown that is dime-sized. I know of others around this age that have "full" heads of hair yet again, there's a little little lack of density at the crown.
You can have the gene at a very small extent, and you could have it the other way and reach the highest Norwood level before you turn 30.