Just to add a little to the discussion of older actors playing younger teens, check these examples out!
Ralph Macchio was 23 playing young teenager Daniel LaRusso in 1984's "The Karate Kid"!!! (I think Daniel San was probably like 13 or so. My goodness- Ralph sure looked it too- hard to believe he was 23!)
And here's another mind-blower. In another 1980s classic, 1986's "Ferris Bueller's Day Off", Alan Ruck played the role of 17 year old Cameron Frye- and Alan was 29!!!! That's just insane! But Alan really did look the part.
And Maria's always been really young looking, at least I think, and even into the 1980s and early 1990s I could still believe she was only maybe in her late 20s.