Sorry to tell you - Northern Irish gun law is pretty much identical to mainland Britain. You are required by law to obtain a firearms certificate from the police to own a gun, as in the rest of the UK. And they will ask for your reason for needing it - just because you want one is not good enough.
Also, civilians are not permitted to own semi-automatic or automatic firearms anywhere in the UK.
So to answer your question - it is not in any way legal to carry a concealed, loaded firearm without a permit. And the only gun you can have of those is the shotgun, if you can demonstrate a reason to the police why you need it.
You can get an air rifle when you're 18 though.
Hope that helps :)