Well, there are a few things to consider about the age of consent. A lot of things, actually. First one must consider the rate by which youkai mature vs when they age, because, being different species as they are, youkai age at VERY different rates.
Then there's also the governance of the realm to consider and if they even have a say in what they age of consent is. Then there's also how getting drunk affects different species, if it affects them at all (which, in some cases, they wouldn't (or if they did, whether they'd be affected by drunkness the way humans would)).
...But by the law of Gensokyo, everyone drinks.