Elbow Lane (on Oliver Plunkett, the pedestrian street) is an awesome microbrewery come smokehouse, but is small and can get very very busy. Market Lane next door is also really good, but you can book tables and they serve the beer from Elbow Lane. The Cornstore is also pretty good for food, as is Liberty Grill.
In terms of pubs, most of them on Oliver Plunkett are pretty good. A lot have music in the evenings too. I’ve been to Cork a lot over the years and never really had a bad night out, have a wander and pick a random pub and it’s normally pretty decent. The attitude to drink really is different over there – in the uk people seem to get pissed and want to fight, over there everyone gets really happy!
A lot of the pubs on Washington Street out to the west of the town are student bars, that may or not be a good thing dependant on your views (if your lad has just turned 18 he’d probably enjoy it!)