Forget CTO. I'm in the exact same boat as the OP, (20 years experience, over 40 years old) and I can't even get an interview for a manager position.

I've been trying to move out of an individual contributor role for a while, but it's always the same story: 1) We need you to build this super-important thing; you're too valuable as a developer right now 2) We're growing fast, we need experienced managers right now (or 2A: Your team is performing at a high level, we don’t need managers) 3) We're cutting back, we don't have a position for you right now. And in my most recent case 4) We're shutting the company down, good luck.

I find most places only want experienced managers, yet the industry as a whole is terrible at providing any sort of career development path for developers.

OP is right - make a backup plan now. If you want to move into management, start laying that groundwork BEFORE you're ready to move on.

Don't interview for a manager. pick a growing startup, ask in the interview about developer career paths, and if management is a separate, lateral, or heirarachical stack (correct answers is "lateral track devs can switch into")

Get good at your job. Get good at the company. Learn the domain and drink the koolaid. And, when the team grows, and they're looking for managers, nominate yourself to begin transitioning. You'll do both jobs and straddle the line for a while but eventually you'll have job experience managing a team.

I think you missed my point entirely. I did those things for 10-15 years, and they led nowhere. Either it's one reason or another from a current employer, or none of it counts with prospective employers all because I didn't already have a manager title.

Sorry, I did miss that. It is unfortunate your employers are not supportive of your career ambitions. I've watched many engineers become managers at PlanGrid, so I know it is possible :)

i.e., have enough saved up to start a startup, and hope to make it big? What happens if it fails? What happens to your retirement, or is the backup plan either continue working till you drop, or rely on kids to carry you thru retirement years?

They said CTO, not founder.