A lot of Covens have age restrictions for maturity and legal reasons, some also have 'red flags' against people who say "I don't want my parents to know" due mainly to legal reasons.
Though if you didn't want your parents to know, don't go on a site called 'Spells of Magic' where it's banner is literally 'Where the world learnsblack magic,white magic,pagan, wiccan and occult arts'. They can check your browsing history and search bar autofill.
Again it is more for the protection of the Covens and the Minors attempting to join. Especially because some Covens discuss topics that are at least R16.
So, Maturity and Legal matters are what drives us to have age restrictions.