Age 24. What is this vertical line going up my forehead? (photo)

A closer, in-person examination would be helpful. However, two possibilities come immediately to mind when looking at the photo. One is a line that arises from static tension of the muscles of the glabella (frown area between the eyes) region. A second possibility is a localized scleroderma condition known as "En coup de sabre.," so named because it looks like the result of a slash of a sabre
For the former condition, Botox would be helpful for relaxing the intense static muscular tension that gives rise to the line. And, if, after years of static tension, the overlying skin has become etched or creased even in the relaxed state, a low viscosity, malleable, cohesive HA filler, as a second step, can be injected to elevate and smooth the residual crease.
If this is "En coup de sabre" and has been stable for a long time, the above HA filler can be used to elevate and smooth the depression. This is precisely what I did with excellent results for my wife who has this condition.
It would be wise to consult with an experienced, board certified cosmetic dermatologist injection expert who can both diagnose and treat these issues. Best of luck. .

The vertical line in your forehead is likely caused by a gap between the paired frontalis muscles of your forehead. There may be more of a diastasis in your anatomy resulting in this. Botox would be unlikely to improve this situation. Filler could be tried, but significant caution must be exercised with forehead filler due to severe vascular occlusion complications which can occur.

The short answer is this vertical line a glabellar rhytid, the vertical lines that are commonly treated with botox injection in the brow area.

It is a bit unusual for it to be so prominent in a 24 year old. The frontalis muscle that goes from the scalp to the top of the brows can have different configurations in different people. In some people it is a continuous sheet across the forehead, in others there may be a gap in the middle. I would suspect your frontalis muscle may have a gap in it, which allows the corrugators (frown muscles under the eyebrows) to create that indentation every time you bring your brows together.

It looks like you also have a horizontal scar in the left side of your forehead.

Thanks for your question
Dr. Weng