If you are asking about numbers in the perception of other people, then the answer appears to be 25, per OK Cupid. They have a question about whether one would date a virgin who is 25 or older. Since the questions on OK Cupid are:

- user-submitted, for sure (they say that)
- vetted by the editorial staff, probably (most likely)

and since OK Cupid has a multi-million user base, the question probably represents the general mentality/trend.

Not that it should matter very much to you, though - you have your own life to live and to make choices that do not necessarily match the normal distribution.