Since bitcoin is just a money why does bitcoin wallet sites has an age limit of 18 years old before creating one?? Does having a money has an age limit?? And since online sites can't even detect people who's 18 below , why do they even bothered it ??
What wallets say you have to be 18? Are you talking about exchanges? It's understandable you have to be 18 to use them as pretty much most places you have to be an adult to use such services dealing with the exchange of money. Trading could even be seen as gambling but either way it's definitely not something kids should be doing. Regardless you can still use many wallets like the main bitcoin one, electrum or blockchain.info etc without any problems so look at alternatives.