Let's not get shouty. there are several possible explanations for why she may get her precise age wrong.
1. She doesn't have a baldy notion cos she was a young kid stoned out her box at the time.
2. She is simply mis-remembering. This is not at all unusual.
3. She
wants to believe she was older as it makes it all a little less sordid. She may well over time have come to believe that she
was older.
4. Or the one I suggested which is kind of like the last one - except I, perhaps a little harshly, suggested she had made herself older to muddy the waters and protect her 'friends'... Messrs Bowie & Page.
Either way, human memory is plastic/pliable. Her birth date and the tour/concert dates which
Thora posted are not. They are checkable facts. Thora checked them. I assume she would be perfectly happy to direct you to where you can check them for yourself.