Abolish the Age of Consent?

In case you don't know, the Irish Supreme Court has recently struck down the law on statutory rape as unconstitutional (the ruling is here) on the grounds that it doesn't permit someone to enter a defence of ignorance as to the other person's age. In Supreme Court-ese: "the exclusion of the defence of mistake as to age is repugnant to the Constitution." Michael McDowell, the Justice Minister is going to propose new legislation to replace the unconstitutional law. The law will equalise ages of consent between genders and will allow for teenagers to have sex with people below the new age of consent (16) provided they are within two years of age of the person who they have sex with.

I wonder though. It'll be difficult to formulate a law that can adhere to the Supreme Court's ruling - allow for ignorance of age as a defence. My feeling is that the age of consent is part of the problem. Unfortunate that the situation is (especially given this sort of opportunistic response to the situation), I wonder if it presents an opportunity of sorts. Why not get rid of the age of consent altogether, instead of adopting the proposed half-measure?

Couldn't it be left to the courts to decide whether, in a specific situation, consent had been given and that the younger/more vulnerable party was capable of giving consent? Obviously, where children are below a certain age, or where an age gap is more than x years, or where one party is obviously vulnerable, it's difficult to think of someone legitimately claiming that consent had been given, even if explicit force was not present. On the other hand, abolishing an age of consent would rid us of strange anomalies where 17 year olds end up on the sex-offenders register having slept with 15 year olds, or indeed where older people predate on vulnerable young people who simply happen to be over the age of consent.

I suppose this comes down to the incoherence of the idea of statutory rape: rape is rape and ought to be punished. But age is simply not a good marker of consent.

Update: I knew I was sticking my neck out with this one: Frank McGahon provides a convincing counter-argument in the comments.