Why do people believe that Penny is 16?

Sounds like the typical groupie, age 15-19 was the norm for following a band like that. Different now, but in the early 70s teens were empowered and more on their own. Funding her own ticket is easy when you have rich friends who play in bands.

Yeah, Penny doesn't look/act like a teenager and she was clearly just teasing William in that scene. Kate Hudson was 21 at the time and I'd say that's about Penny's age.

Some of the groupies of the time were as young as 13! Penny is based on the actual Pennie Lane Trumbell who started seeing bands when she was 16. I think due to moral standards they would not have been able to straight up say she was 16 in the film but there are hints along the way. She most likely had wealthy parents or the ticket was bought for her by one of her famous and wealthy admirers.

How can she afford to be a lone girl? She is being supported by the bands in the end, she supplies sex.. errr.. support and in exchange she gets to mooch off them.

She wasn’t 16. She kept saying “Me too” because she knew the kid was lying when he said he was 18, 17, and 16. She didn’t say “Me too” when he said 15 because she figured 15 is his real age

She was lying, obviously so. It was obvious that she was just saying whatever the man she was with wanted to hear, because that was how she lived her life, bounding from man to man and telling him whatever lies seemed most convenient at the time, because that was her job. That's all she did, float from one man with money to another, and never getting much out of her relationships except more time spent traveling with some band, more time in which she could tell herself that she was living the life and wasn't just being aimless or running away from something.

So she lied about her age and her name and everything else because it got her what she wanted, but also because she didn't want anyone to know who she really was. Or who she had originally been.

A lot of the groupies of the time were underage. It would not have been unheard of but they probably couldn't make her 16 in the film and behave the way she did. She would have someone buy her the ticket to Morocco for errr services rendered...

Either that or she had wealthy parents who she was mooching off.