As a matter of fact, in no US state can a CHILD decide which parent to live with. Only a judge can make that decision. A chld (under 18) can voice their preference but its left to a judge to make the actual decision. Some states do codify how much weight a judge must place on the chld's preference, but the judge must still make their decision based on the best interest of the child.
I haven't been able to find a definitive answer for Ireland, but what I have found seems to indicate that the laws in Ireland are similar. It is clear that juges are supposed to decide custody according to the best interest of the child. What's not clear is whethere there are any laws that say a minor can pick.