I think the relationship should be mutually respectful. If he is much older and you are treated like I subordinate or child in the relationship then it is a problem. Do you have equal say in the relationship? Are your needs being satsified?

If the relationship is long term, later in life a large age difference may make a difference. Let say if he is 20 years older, when you are 40 he would be 60. At that age difference he would be at a different stage of life. You would be becoming older but still productive and he would be going into his golden years and his life would be winding down. At age 60 your body starts to age much faster than earlier in life. Just something to think about.