This is what happens when you write a story arse about face. The original trilogy positioned Obi-Wan as as a mystic/mentor, Merlin/Gandalf character, rather than a grizzled veteran (Alec Guinness was badly miscast here). This, among other things established in the original trilogy, imited what could be done in the prequels without evoking fan screams about violation of canon. That said, there was no reason why Anakin should not have been introduced as a teen/young adult. Also no reason why he shoudn't have had a father (the most off-putting, WTF part of that film, next to the robot armies!).