AD it is possible to make it in GA after airlines, but those I've met have mostly been at or near the end of their airline career. The notable exception was the airline pilots who found themselves financially distressed in 1989 and drifted back into GA. Some stayed and did OK but most moved on to other pastures. Some moved out of the industry all together.
Which brings me to this hackneyed phrase: flying is the best job in the world, and the worst career. This is especially true of GA which is so very cyclical. The peaks are very high and the troughs very deep. Be prepared to lose your job or be under employed at least once and you will probably be kicked on your way up and on the way down too. Not many GA pilots get to take Long Service Leave. (I know there are exceptions, and you guys prove the rule.) The point is, keep your other skill set sharp. Be prepared to fall back on your other skills to put food on the table when times are lean or things turn ugly.
I don't see any reason why you can not have a successful shot at GA if you really do want to give up airlines. You will just need to start at the bottom, like everyone else and work your way up. Frankly I think a lot of operators would view you quite favourably because you are not likely to be enticed back to airlines and you have some proven experience in persevering with a structured training and checking programme - something that is becoming ever more relevant in GA.
I recon you should enter GA via an instructors rating. Start in one of the pilot factories and stay there until you have an A Grade or Grade One (or whatever they call the things these days) instructors rating with IFR and Multi Engine training approvals. When you have these qualifications you will have opened up a career within GA. You will be looked at twice by potential employers, with a view to having you involved in training and checking and you will be protected a little from the troughs I mentioned earlier. (You will still do plenty of line flying, in GA you always will).
Have you considered a career as a military pilot?
All the best with whatever you choose.