I've never previously encountered the term 'flames of rebellion', but I like it. I definitely have these flames, though that's not necessarily notable as I'm only in my early-20s and still at a relatively liberal university. It's worth mentioning that these flames are something I value and would like to maintain, thus I have been considering how to keep them alight. Is it possible to keep them alight?

One solution I've considered is to keep oneself outside 'the system', as such, while youth is fading. e.g. if one completes tertiary education only to jump straight into a 9-5 office job, it seems unlikely that one would maintain focus on rebellion. This seems to tie in with the idea of having "interest...vested in a way of life", as you mentioned--your focus/interest shifts to your job, and your job relies on 'the system'.

Failing that, the second solution I've considered is to actively surround oneself with others who also have the flames of rebellion. This is obviously easier when younger; your mentioning of your friend losing this trait seems to be evidence that surrounding yourself with such people is not going to occur naturally--it needs to be active. So the task would be to join organisations or groups or communities which are likely to draw such people, and which are relevant to whatever ideas of rebellion resonate with you.

My personal planned strategy is to attempt volunteer work in teaching English as a second language overseas--I've not yet thought about what to do after this; my hope is that it comes to fruition before I lose my flames.