It depends who you ask - everyone has their own opinion on this subject.
Some people think it's acceptable to have sex under 16, others wouldn't dream of doing it before they were in their late teens. I honestly think it depends on what kind of friendship group and family you have.
Generally, 16-24 seems like an average age for losing virginity, but that's not to say that at any other age it would be "weird" to still be a virgin.