Both. Too many convince themselves their relationship is solid enough to handle it, when it is not. Most are not ready to go from fantasy to reality. Age doesn'treally matter. When they do jump in, they don't know how to deal with the emotional storm after the deed is done.
Starting slowly and dealing with the emotions as you gradually work your way up from mild to wild is the best way for most people, but if you have been in the lifestyle for a while, you know that it isn't just single men that are impatient.
There is no truer phrase than "Be careful what you wish for "