A Mooney is a lot of airplane for a new pilot….and the insurance costs will reflect that. You should check with your intended provider to see if they will even insure you. They might well require something like a babysitter for your first several hundred hours. If you wanna try out aircraft ownership, you might look at buying a Cessna 150 or Cherokee 140 to use during your training. It would give you a taste of what you’re up against owning an airplane and it could potentially make training slightly cheaper if all you need to do is hire the instructor. Of course the trade-off is you’re on the hook the operating cost of the airplane. just because you weren’t paying them in rental fees, doesn’t mean you aren’t paying them.
IF you decide to pursue the license and the Mooney, find a school that will start you from day one in complex, high performance aircraft. It will be EXPENSIVE but you need to develop habit patterns and experience with retractable gear and constant speed props from the start. Part of the reason the military can train people in such a short time is that they start out in very complex, high performance airplanes. Time spent in a J3, while making you a good stick and rudder guy, won’t teach you the systems and energy management skills you will need in the Mooney. In any case, a flight school is probably a better choice than an independent instructor at the local airport unless you can carefully vet the independent guy (all my time as an instructor was essentially as the independent guy so don’t think I’m saying they can’t provide good instruction.). One thing about a non-school affiliated instructor, if you are in a big hurry and want to fly A LOT, they can usually go faster than a flight school program.
With all due respect, given your age, pad every timeline any training center gives you by 20%. It’s not that you can’t learn but you likely learn less quickly than your 20 year old self would have. In several thousand hours of dual-given, I never had a second-career, older student who learned as quickly as a young student. However, older people are typically much better students so they were easier to teach. Take that for what you will.
Aside from that, go make sure you can pass a third class aviation medical before you spend money on training.