New to the Forum Looking for Direction

It sounds as if you have a good leg-up on others who may be trying to start in the industry. The best advice I can offer is to get yourself to Ft. Lauderdale (spring/fall) or Antibes (summer/fall) and start meeting crew agents and brokers, and hitting the docks.
Your age will hamper you, only if you let it. I started in yachting at age 23, and started as a captain. Confidence (not misplaced confidence), respect, and finesse is the way to overcome dealing with skeptical owners and older crew-members.
And if yachting is a really what you want to do, get off the workboats ASAP. As much as the driving experience is beneficial, the overall feeling is that workboat guys are too rough around the edges for yachting. Ours is a hospitality industry as much (or more) than a marine-based business.
I wouldn't worry to much about stability. Boats are bought and sold, but someone always needs a captain to run them. When one door closes, another opens. Just save up for those rainy days so that you don't have to take a less-than-ideal job out of desperation.
Last bit of advice- get some practice at keeping your receipts and accounting for your expenditures. This skill goes a long way in this industry.

I'll answer the stability question first. The situation you described is exactly what happens. A job can be for 6 months or 10 years.

Now, it's likely you'll need to serve under another captain at first, perhaps on even larger boat. Some direct yacht experience will help.

The industry can be great. You can enjoy yourself in it and make a lot of money. However, it has it's negatives too. Many very long days and weeks. Time spent away from home, not even always truly having a home other than the boat. Now, you won't face the same as if you were chartering. Still it makes it difficult to build personal relationships.

The delivery business depends on you and your reputation and connection. I know people who do lots of deliveries but they're established and the first person called by people like Hatteras or Hinkley or Outer Reef or Hargrave.

Age is an issue only if you make it one. Maturity is an issue regardless of age. If you land in Fort Lauderdale or Antibes, your job interview starts the moment you arrive. It includes where you live, especially if in a crew house, includes as you talk to people, even includes where you go to dinner or to relax in the evening. Someone ultimately important to you may notice, good or bad.

We've hired four captains. Their ages at hiring were 55, 52, 29 and 25. Interestingly, all four new at an early age this was what they wanted to do. The 55 and 52 year old (husband and wife) both started as deck hands and then mates on fishing charters when they were in high school. The 29 year old spent a lot of time on her parents' boat growing up, working for a charter company during summers in high school and college, got her first license at 19, and became full time in the industry as soon as she graduated from college with her accounting degree. The 25 year old only got occasional exposure to yachts as a child, but loved every aspect and immediately upon high school graduation set a course to be a captain. Her first job was on a boat owned by a friend of her mother, a boat she'd been on with her mom. Her first job as the Master on a boat was a referral that boat owner made to one of his friends who had a smaller boat.

Ken pointed out two important factors. Yacht captaining is a job of many hats and operating and handling a boat is just part of it. It is most definitely in the hospitality industry. And you are also managing a business. Seamanship is important but so is the ability to work with others, to manage others, to serve a customer, and so are organization skills, and planning skills.

You need to talk to some people in the industry face to face, perhaps even find someone willing to mentor a bit, or willing to let you join on a trip just to see how things are. Right now you're talking about a field you really have very limited knowledge of. It's like any profession in being far different from the inside than it appears on the outside.

One other comment. When making a career change you must always be prepared to take a step back in pay, in income, initially. This is no exception. You're experienced in your current profession, not in the new one so why should you make as much?