Mature men aren't generous with the words "I love you". They will wait until they absolutely mean it and can follow up with an actual relationship (of course there are those that will say it just to sleep with you, but they don't fall under the category of 'mature').
If he hasn't said it to you yet, it's probably because the future of your relationship is still so uncertain and he doesn't want to really 'commit' to you just yet.
Live as if you were to die tomorrow. Learn as if you were to live forever. - Mohandas Gandhi