Now, I am going to play devil's advocate here for a moment. I have met plenty of people who have been diving for 30 years and they are horrifyingly bad divers. It's not just me either. Ask Rob, Mr. Tom, Bryan, Henry, Herman, Bill, and any number of other guys on the forum. Just like anything in life, you can dive for a long time and still be crap at it.
I rowed at the gym yesterday next to a person who had been rowing "for 30 years" and their form would have gotten them laughed at by any amateur crew team, and possibly savagely beaten.
If you want to make sure that there is no Dunning-Kruger in action, then at least have someone whom you trust and know is good at diving go with and give you honest feedback on your abilities. A lot of people, including a small minority of people on this forum, think scuba instructors are in it for the money. I promise you, the money is shit. I make more billing .5 hours of IT work than I do teaching an entire advanced class with 8 people in it. Sometimes, regular divers think diving is a scam. It is, but it's a scam that's not making any instructors any money. It's making whatever venture capital firm that owns that diving agency money, so they can sell them to another venture capital firm. There is, generally speaking, no money in diving unless you find it on a wreck.
Dive shops don't really make any money either. That's why there are always a crap ton of them for sale:
http://www.divecenterforsale.com/
Now consulting...THAT's a real scam.
The short answer is if you haven't been diving in a long time, then have an adult, in some form, check you out and make sure that you are not terrible at it. I say this sincerely.
The impossible missions are the only ones which succeed. -JYC