CobiTBM I think people in or around their 30's have two teams (as such) is mainly due to when we were a kid
Nothing to do with being in your 30's, it's most kids in general. They tend to go with who their friends support. When I was at School it was Man Utd, Liverpool or Arsenal. Nowadays it's Man Utd, Chelsea, Liverpool, Man City.
As you grow up and realise your town has a football club and you start going, you then fall in love with them and they become 'your' club, but you might still follow the club you supported as a kid.
I dont entirely agree as i see far more kids these days wearing Reading shirts than i did back in the 80's......as said, back then unless you were taken to Elm Park to watch Reading then you would normally support the teams you saw on TV/in your sticker book etc