It's not possible for every 25yo programmer working today to become a consultant or CTO by the time they're 40 (or in fact any age). There's just not that many

It's not possible for every 25yo programmer working today to become a consultant or CTO by the time they're 40 (or in fact any age). There's just not that many CTO/consultant jobs! Similarly, not everyone can become a project manager, product manager, head of engineering, or whatever. So as you age, you can take one of those career changes, or just ... find a long-term niche and stick there or keep up with what's new, and sell your experience. There is a world beyond single 25 year-olds working stupid hours in startups.