20 is not too young. I was always sitting out it in the sun trying to cure my acne.
I think maybe the TEXTBOOKS and Doctors didn't see rosacea as much back in the day because of possible factors such as food and weather conditions. Just a theory.
I would say shield your face from the sun, stay relaxed, and sweat in places where you are in control of the environment. Like a hot tub, raising up if you ever feel your face getting too hot. IT works great for me.
ALso, coconut oil, just a small amount, rubbed on the red areas, does great. small... small amount.
THings I wished I would have known at 20. And I wouldn't have done anything like Metrogel, antibiotics, or Differin.