I've seen a number of "age-gap" relationships turn out well and believe that they're certainly a possibility, presuming both people are adult. On the other end of the scale, a seventeen year old young woman in a relationship with a fourty-five year old man is not something that's likely to develop into a lasting commitment.

I would suggest that you tell him how you feel, but only if you've proceeded cautiously and know that there are genuine feelings present rather than more minor, passing feelings.