Huh, this is actually super plausible and Harry is unknowingly making it far easier than it could be. By acting in adult-like and weird ways all the time, if Quirrell takes his place far fewer people would realize than if he was a regular boy. Though I think a form of possession is probably more likely than polyjuice based on the hassles inherent in polyjuicing someone for long periods.
Huh, this is actually super plausible and Harry is unknowingly making it far easier than it could be. By acting in adult-like and weird ways all the time, if Quirrell takes his place far fewer people would realize than if he was a regular boy. Though I think a form of possession is probably more likely than polyjuice based on the hassles inherent in polyjuicing someone for long periods.