My cheeks are incredibly flat. I'm a young male and it makes my face look old and flat. How do I fix it?

I suggest you see a cosmetic dermatologist with expertise in treating younger males.  This is a very common area that needs addressing at young ages and can do very well with appropriately placed fillers with cannulas. I would avoid implants. I suggest a formal consultation.  Best, Dr. Emer.

Without photos, I am not sure what you mean by "sagging" eyes. However, without cheek support, I would guess you are referring to a descent of the tissue beneath your eyes. And certainly, cheek implants would go a long way to dramatically improving your look. If you are still timid about that, you could have saline injected into the appropriate area to give you a temporary idea of what it would look like.

Cannot comment accurately without at least seeing a photo. Best to get in person consultation.  Sometimes, fat or filler injection is the answer. Implants may be another option. If there is bulgy eyes, then orbital decompression is another option.