According to the National Institute of Mental Health (NIMH):

• 20% of youth ages 13-18 live with a mental health condition.
• 11% of youth have a mood disorder, a category that includes depression.
• 50% of all lifetime cases of mental illness begin by age 14.

More information from the NIMH about teen depression can be found here.

Note — The image in this post was taken by Tiago Bandeira, and it was obtained from Unsplash.com.