To tell you the truth, at school I was taught to pronounce this words as a "teenAger", maybe because of my native language, but then, I constantly heard "tEEnager" and got confused, which one is correct? As some of you have mentioned it has 2 stresses ( compound nouns usually have 2 stresses - main and secondary). Buuut the main is on the 1st syllable - ˈ'ti:n,eidʒə. So to be on the safe side, look up words now and then, even if you're 100% you're right how to pronounce them,