If you want to be an IC, don't short change your accomplishments. Eng Mgr is not a promotion from IC, it's a career change.
The SWE career progression is much more established, and is often much more formal and understood than an Eng Mgmt track.
Your younger manager has recently gone through a significant career change that requires a significant amount of self-education to advance further. It's possible he'll advance opportunistically (if there's a vacancy) or by being clever or political, but his competency will not necessarily advance with him without him putting a significant amount of effort into learning this new career.
It's not uncommon for established SWEs to make more than engineering managers until the engineering manager has progressed to a level where they are dealing with levels of stress (business & social) that would make most people's hair fall out.
Even then many companies have career tracks that pay as well in the upper echelons for individual technical contributors as for high level eng mgrs. The one thing they have in common is that there are very few positions at the top of any career ladder. It gets competitive. Hopefully your aspirations match your talents so that you can compete for those fewer positions.
There is nothing special at the top of the ladder, just more money sometimes. Money isn't the only way to build a good life, and that's all money is good for.
Point being, don't blame your age. And don't underestimate yourself. And definitely don't compare yourself to others. If you are growing, then good fucking job. Keep doing that and maybe switch positions to somewhere more conducive to your growth if you feel like that's necessary.
I’ve been an engineering manager for over three years; and the skillset is completely different. So much so that I recently flubbed some easy LC questions.
Businesses may treat it as a promotion, but don’t make the mistake of thinking it really is one.
Which for me means that you don't yet know what advantage these 'wasted' years could give you in the future. Just trust yourself to make the best decisions you can given the circumstances and you'll get to where you want in as little time as you can.
You have an opportunity to distinguish yourself. You already stand out and break the mold as someone with a nonstandard background, and it will get noticed—and treated differently—if you excel.