Can teenage love last forever? It surely feels so when you are a teenager, of course. But can you really distinguish between true love and boiling sex-hormones? Cause those are in action, those are the driving forces when you are a teenager, even though we never acknowledge it as being so. There is a fine line between loving and sexual urge, but when we are younger and just discovering the content of our trousers, everything seems to be love. With big L, naturally. And big everything. 
However, the sentiments experienced when we are young are based mostly on physical attraction. We hook on that strong sexual urge other correlated stuff, like love. Facts say that couples marrying high-school sweethearts have the least chances of actually remaining together, compared to couples tying the knot later. 
Simple answer: there are slim chances that what you find attractive and intriguing when you are 15, will continue to think it so later in life as well. Why is that? Because what you find irresistible when you are 2, won't find similarly interesting being 5, 10 or 25 years old.
People change, needs change, interests change. It is almost certain that the guy you dream about in adolescence won't be the one you dream about when you are over 30 years of age. You will find yourself wondering how it was ever possible for you to like that specimen in the first place.