I am positively baffled you did not continue networking with the people you did business with or worked for you and that after only 4 years, you are soliciting employment with strangers who are presented with no way to verify that you have done anything professionally for the previous 16 years.
I bet who ever you approached for employment was highly suspicious of someone who at middle age did not have a verifiable employment history and had a story that they are just a bored, energetic, independently wealthy person looking for something to do.
I certainly don't doubt your story but you must understand how somebody else who has no idea who you are and cannot verify your past might.
Advice from a specialist in the professional headhunter business would be beneficial if you insist on continuing to seek work as an employee for someone else.
Personally, I would never be satisfied working for someone else after having been in business for myself these past 15 years nor would I expect to be able to fit in with the office politics. I would want to start another business.