Yes it's dodgy, it's also illegal and you can get into serious trouble, i think you are underestimating how serious it is.
It doesn't matter if he looks like you, he is not you, not to mention you'll get him into trouble as well.
Besides, they will be able to tell that it isn't you simply by looking, or you'll be caught out.
You'll just have to wait like other people have to.
I started college at 17, everyone else was 18 but i had to wait till i was 18 before i got my Garda ID
Besides you shouldn't be in bars and clubs underage after 9 anyway
You can apply for a passport anyway, and you won't have to wait about for Garda ID after you have turned 18, but definitely cannot fake that either