I don't think they ever actually established Anakin's age when he turned. I never thought of the Shaw ghost as Anakin before the fall. It was the redeemed Anakin. Showing his young form from when he was an uncertain person who fell to evil kind of destroys that. This is the jedi he should have been, not what he was. What's worse is that they used Episode III footage to do so. Hayden wasn't even aware he was in ROTJ until they showed him. It sounds like a last minute decision to me, not Lucas begrudgingly restoring an idea.