I turned 23 and I have noticed "dents" above my eyebrow. And I also have a deep line in between eyebrow. (Photo)

HI Chic.The glabella is the area of the face that is made up of five muscles. The procerus is in the middle and there are two corrugator muscles on each side. the corrugators move in towards the procerus to give you the "dent" and the "line".  I would start with 2 units of Botox in each muscle and I think it will relax those for you. It will last about three months. 

Dear chic23:

Thanks
for sharing your photos.

The corrugator
muscle is one of 3 muscles in the glabella group of muscle between the
eyebrows. The reposition the eyebrows into a "down and in" direction
by contracting the skin to the bone at the top of the nose creating an angry or
scowled appearance. It also pulls the forehead and inter-brow skin toward each
other in a vertical single or double furrow or line.

The edge of the corrugator muscle can extend
significantly upward and outward to the lateral forehead. When it contracts, it
can produce one or more dimples over the brow depending on its interaction with
the frontalis and orbicularis muscles.

The FDA
approved Botox and Dysport injection technique does not adequately address the
contraction of this muscle extension and the additional recruitment of skin
towards the middle.

It will
take a well experienced Board Certified Injector to understand the dynamics and
interplay of these muscles of facial expression to know where and how deep to
inject muscle relaxers such as Botox.

I hope
this helped. All the best!