Is 18 too young for brow lift? The eyebrows droop in front of my eyes, making me always look very cross, angry, and tired.

You are correct that most 18 year olds would not be good candidates for a brow lift, but you would either need to be examined or pictures of you would be needed to determine if you might be a candidate for the procedure or not.  It is also possible to get a small degree of brow lift from Botox injections or from Ultherapy treatment.  

Browlift for sagging brows in the young is something that i have done for 35 years. Some people are born with sagging brows like ears that stick out. I need to see photos though to know if you are one of those people.