I am not a professional detailer and never will be. What I am is part of the market you are trying to reach. My daily driver is a 7 series BMW and I own/owned a number of other classis/custom cars.
Please don't take my candor in offense, it is not that meant that way, just trying to give my advise from some one in your target market group.
Nothing wrong with a Corvette, but I don't consider them to be a 'high end' car. For that matter, many BMW's. Merc's, Rovers etc. When I think high end, I am thinking classics, bentleys, maserati, etc, etc. But, that really makes no difference here.
Your age is working against you. Sorry, but it is. I have been working on cars both as an enthusiast and even semi-pro in racing teams since I was 13 as well and those 33 years does not mean I am an expert. Citing repeatedly that you know what you are talking about and have been working on them since you where 13 is of detriment. Combined with the repeated "I know what I am talking/doing" for me underlies the age issue that already exists and quite frankly, sound a bit arrogant.
I don't know what your shop is like. If it is a personal residence, that is a negative for me. I do use detailers that do the work at there homes but for reasons that are to come.
High end car owners like to be catered to. The like the have the car picked up, they like to have it delivered, they like to lay down the plastic (can't tell you the last time I had cash) and be done with it, they expect results and they expect them everytime. They want personal, prompt and frequent communication. They want what they want and they want it yesterday.
They tend to go with the good ole boys club. You have to get into the club and once you do, they will refer you so long as the service is excellent, ever single time.
Actions speak louder then words. You send they not to believe what you are telling them. That is in part because of some of the factors above. So fine, prove it to them. Find 'high end' enthusiast clubs/shows and show them. Seeing is believing. If you show up and demonstate that you are a pro and they can see and touch the results for themselves, they may give it a thought. You could maybe do a 50/50 car in advance just so they can see what you are talking about. Down side is, many of these clubs are also enthusiast and tend to be hands on themselves. So don't show them how to do it! Although, they may appreciate being schooled on maintenence. But, I would reserve that for paying customers.
Another thing with these clubs, if you find that is a large one just ripe for the picking, find the president of the club and find out which car is theirs. See if you can make a big difference in thier car and if so, offer to do it for free to demonstrate your work. Deliver it to the next meeting after you are done. So, everyone can see for themselves.
Keep at it! Strive for perfection, cater to their whims, demonstrate all the attributes of professionalism and make the contacts. If you do it, they will come.