There are good general rules in a few comments here, but I think it's ok to say that in 2018 the specialization arrived to a point where system/low-level is too large to reply in a good way? One thing is to write games engines, another is to write networking code, yet another embedded systems, device drivers and so forth. There are certain common aspects, but the details of what you need to know change significantly.
On that, unless you ABSOLUTELY love games and game engine design... the field is relatively flooded and comparative pay may not be great. Not to discourage, but making a decent living isn't a bad thing.
