Fermenting anything generally results in at most some 15-18%, depending on the yeast you use. I'd say 10-12% is more realistic for homemade wines, but 14-16 isn't out of the question.

So I don't know what the deal is specifically with dandelion wine, but usually 10% alc will fuck up a person (and a teen especially) pretty well if chugged and the brewing process usually leads to there being all sorts of things in it (alcohols sugars, not-too-toxic byproducts) so the hangovers you get from home wines are usually.... interesting, to say the least.

We to drank way too much, got way too drunk, and it had an awful hangover