Military aviation is out, he's way past the age cutoff + waivers (not many waivers these days anyhow).

For the OP, yes it's entirely feasible, age is not an issue especially given the clear demand for pilots due to retirements over the next 10-15 years. Where age can be an issue is older folks tend to be less flexible as far as moving and lifestyle (family, financial obligations) so they tend to not be as aggressive at making the career moves needed to progress (or jumping through major airline application hoops).

1. No family makes it easier. Ideally you wouldn't have any obligations like real estate which would keep you tied down somewhere.

2. It's good that you already fly. Anytime someone talks about blowing a bunch of money on career training, I tell them to go get a PPL first and if they enjoy it then come talk to me. If you don't have one, I would get an IR on your own before you commit to a career. If you struggle with that, 121 aviation might not be a good fit for you.

3. Given the rapid pace of hiring and career progression, at your age I would probably do an accelerated program (pay out of pocket if at all possible). Get your seniority asap. When I was in your almost exact shoes years ago I took a more measured approach, and that paid off when everything came to a screeching halt for about ten years and I had to stretch the finances for longer than planned. But in your case, that situation is very unlikely. The retirement numbers do not and cannot lie...unless the US airline industry shrinks by about 70% hiring must occur. They might dull the edge just a tiny bit by extending retirement age to 67 but that's about as far as it will go IMO. Even if they extended it to say 70 there would be few pilots who desire to work that long, and even fewer who could pass a medical.

Easy to get CFI jobs. Very easy. Just don't sign any sort of training contract unless...

1) You're CERTAIN it's a good place to work AND
2) The contract will expire before you reach airline hiring mins.