Are my boyfriends reasons for "not being ready for marriage" valid or just a way to stall?

My boyfriend of 2 years and I are very much in love. We are both divorced (he for five years, me two 1/2 years) and we have a long distance relationship - two hour drive away - yet spend most weekends together. I have younger children, his are grown, his youngest has two more years of college. I have brought up marriage. .. "where are we going with our relationship", etc. He has stated that he is not ready for marriage for at least two more years mainly because he wants his son to have the option of living home next summer (his last summer before college grad) rather than a new household as well as finish financial obligations to his son's college and alimony to his ex-wife. I have met his son several times and he and I get along just fine. I have a very decent income that I would bring to the table - he makes excellent money himself. I guess what bothers me most is that he doesn't ever talk about "when we're married one day" or "when we get married in two years", etc. I don't question his love, fidelity or commitment but I am starting to wonder if I"m wasting my time or perhaps we're just not in the same place commitment-wise. His excuses aren't insurmountable enough to post-pone marriage for two more years. Love shouldn't be this complicated - we are both single, we're in love, been dating long enough to know each other very well, etc. He is in his 50s and I my 40s so I am wondering if I should just move on?