I'll give you a clue: HERE. Now what he superficially seems to be saying sounds emminently reasonable. That there is a difference between someone aged 17 having consensual sex with someone aged 15 and a half and someone aged 45 having sex with a 6 year old. I agree with that, of course there is. Three things though:
1) The law already recognises the difference between thse crimes. Both remain crimes but the latter incurs much more serious penalties under UK law.
2) He's suggesting the law should be changed for GIRLS from 13 up. Surely if a girl is capable of binding consent at age 13, so is a boy of the same age. There are countries in the world where the age of consent is different for boys and girls. I think that's a bad idea. I think that's sending out a message that the sexes should have different concepts of sex. And that's unhelpful.
3) He's talking about relaxing the law for men who have sex with girls from 13 up. If he means to relax the law for men and women who have sex with girls and boys from 13 up then I'm prepared to talk. However if he's relaxing the law the I think there a good case for allowing it to be applied up to a higher age limit. Say 15 to 18 year olds can have sex with someone up to five years older than them, no more. Personally I think the law is better as it is but there may be a case to be made there.