The Air Corp is a good idea if you can get flying with them. They'll train you well and you'll get your hours up. Also, employers like the discipline and high quality of training the ex-air corp staff bring with them.
I went to college and became a chartered accountant, now I'm going back to study for my PPL and ATPL (hopefully). The benefit of the route I took is that I have a fairly decent job which allows me to pay my way through the flight training. It's also a great fall back position if the flying doesn't work out.
Education is always a good thing to have, do your best in the Leaving Cert so at least you have options.