A term basically saying that
it's alright to at least be attracted to a person as long as they've gone past
puberty. Obviously "grass" refers to their "bush" or pubic hair. Would typically be applied to, for instance, a girl maybe 13 years old and up. Can often be used in reference to
actual sex (intercourse) but not necessarily.
Man#1: What's the youngest chick you would ever be into at your age?
I mean what do you think is "okay" to fantasize about?
Man#2: Hey man. Like my coach always said: if there's
grass on the field, it's time to
play ball.