Very often there are people that choose to enter the work force after high school instead of starting college. Many of those people decide later in life to go to college and get a bachelors. I believe this usually happens in your late 20's to early 30's but it's not unheard of to have people in their 40's in college. To me it seems like this isn't an unusual occurrence for state colleges and many universities but it seems that it would be much for difficult for this type of student to enter an Ivy League.
The chances of being accepted into an Ivy League are always small, however is it much harder on an older student? I believe there are exceptions for people that enter the military but I have a feeling that even a brilliant older student would be wasting their time applying to an Ivy League for a BS.