Yeah, i know exactly what you mean. Well, it don't really matter squat here..you're viewed as a 1st year undergraduate. Meaning that if you do get college residences (likely enough, but hard to get), you'll be stuck in Trinity Hall (Rathmines) which is about a 30 min. walk to campus. They're really nice, but yeah...it would be like living in dorms with underclassmen. Or, you could get Goldsmith Hall... which isn't exactly the nicest. Rooms are "cozy." Also, if you get rooms on campus one year, it will be unlikely that you'll be offered rooms for the rest of your years here. So some international students live on campus (goldsmith or trinity halls) for the first year and then find apartments. Others find apartments straight away and if they want to, shoot for rooms in their final year (most don't). The place to look for apartments is
www.daft.ie
For Trinity, look for places in Dublin 2 (dame street, merrion square) Dublin 4 (ballsbridge, donnybrook), Dublin 6 (rathmines, rathgar), Dublin 8 (christchurch). The first two can be pricey, but could be affordable if you found people to live with. They're nice areas. Rathmines/Rathgar are very student-populated places. A good walk to college, but a short bike/busride (although you want to cut on transportation costs as much as possible). Christchurch and places surrounding (Patrick St, St. Patrick's Cathedral) are about a 10-15 min. walk and perfect because it's between Trinity and St. James's Hospital, with a bus route v.close to tallaght hospitals too.
Dublin is funny though, because there are pockets of bad areas. for instance, I would not really venture onto the north side of Dublin (except Smithfield and IFSC, I don't know what Dublin region those are). Also, places past Christchurch (ie Thomas St and St. James's, but Kilmainham could be ok).
You'll learn more once you get here.