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

Many options are available to you from neurotoxins such as Xeomin and Botox and several browlift options.  I would suggest consulting a board certified plastic surgeon to determine your best options.

The indication for a brow lift is true brow ptosis. Like rhinoplasty, the patient  should have completed their growth spurt before elective cosmetic brow lift surgery

Without photos, it is hard to be more specific, but in general terms, there are a few, simple nonsurgical approaches, which include the injection of microndroplets of neuromodulators, such as Botox, Dysport or Xeomen, either alone or in combination with volumizing fillers injected finessefully in particular locations above and below the brow (The Nonsurgical 3D Vectoring Browlift) that can restore lift and proper projection to droopy eyebrows. I have found this combination approach especially helpful for younger persons with premature drooping and sagging of the brow, which seems to be the case here. The entire treatment usually takes no more than fifteen minutes to perform and engenders little to no downtime.  For more information on the above, I suggest you check out the archives of Realself.com.

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.

If there is some physical obstruction of the vision or the eyes are always tired then the right age is when you become a consenting adult.  An 18 year old can certainly have enough of a problem to need correction.  The brow can be heavy from aging or for congenital reasons.  With some patients a slight elevation of the brow can be achieved with Botox injection to the lateral depressors of the lid which will also reduce crow's feet.  This would be a modest improvement and would only last about 3-4 months.  If the hairline is in a low position then an endoscopic brow lift is the best choice.  If we need to keep the hairline position undisturbed then an incision can be made at the hairline.  Pictures would be helpful in providing you direction toward the best option for you. 

It is difficult to give you a full assessment without any
photos or an in-person examination.
However, your story is a common one that I hear in my practice, and it
is certainly treatable. The aesthetic
ideals for brow position are right at the supraorbital rim in males or just
above the supraorbital rim in females.
There is no definite age-limit for a brow lift surgery, but most
surgeons would try to avoid performing surgery on an 18 year old. One option that you have is Botox
injections. Botox works by paralyzing
the targeted facial muscles. Injections
to the glabella and eyebrow depressors could give your brows a “chemical brow
lift.” This type of treatment would be
quick, easy, and most importantly- temporary.
If you like the treatment, then you can continue to do it. If you don’t then the effects of the Botox
will wear off in a few months, and you never have to do it again. I recommend that you find a board-certified
facial plastic surgeon for a complete evaluation and discussion of your
treatment options. Good luck!

While there is not an age requirement for brow lift, there may be a number of nonsurgical options to consider first. Consult with 3 board certified plastic surgeons to understand your options. Do not rush into surgery.

a browlift can be done... but it has to be confirmed by an exam and hearing your expectations.  Schedule a consultation with a local doctor to find out what options are available for you.

You have several options, including brow lift surgery. For true brow ptosis, you can try a nonsurgical brow lift with Botox or other neurotoxins, such as Dysport or Zeomin, with possibly some fillers to temporarily lift the brows. Otherwise I usually perform an endoscopic brow lift, which requires in depth consultation to cover all of the aspects of this procedure. It does have a high patient satisfaction rate, and excellent longevity.