Sounds to me like he doesn't want to ruin a good thing. If you are....say...16, and you get together, your relationship probably won't last, because you are young, and immature, and rarely do 16 year olds stay together. Now, if the two of you wait until you are...say...18, then your relationship may have a chance of turning into lasting love. If you wait until you are 20, and both have good jobs, then your relationship may bloom into marriage.
Maybe he cares so much about you, and thinks so much of you, that he wants to wait until something will come of your relationship before persuing it. Maybe he's decided that you are "the one" and he wants to make your relationship work...and as far as he knows, the only way for that to happen, is by waiting.
Maybe his parents won't allow him to have a girlfriend.
Maybe he thinks that you'll want to have sex, but he's not ready, so rather than be all embarassed about it, he just decides not to date you.
Maybe he likes things the way they are, and now he's afraid it's going to change.
Tooooooooo many possiblities.