That's an interesting question and one I've honestly never considered.
I'm not sure my recalcitrant streak was sufficiently developed at six/seven years of age for it to be the primary reason, at least consciously. My first game, in fact, was at old trafford in 1976, united v Ajax in the UEFA cup that my dad took me to (Lou Macari of all people, scored), but I wasn't that arsed. Certainly wasn't on the hook after that game. My first game at Maine Road came later that year v Coventry in December of that year (when I'd just turned seven). I remember Dennis Tueart scoring. My dad's younger brother (so not quite a 100% red family, although near as damn it) took me. Sat in the Maine Stand to the left of the half way line. I can smell the cheap cigars now. Maine Road captivated me and felt much more like home, plus I loved City's colours, so I think the answer is probably 'no', but who knows in all honestly. Could have been a 'sliding doors' moment, or maybe not.
Whatever my reasons I'm so glad I took the path I did. Being a blue is so much a part of who I am. It's one of the things that most defines me as a person. I certainly couldn't imagine supporting any other team.