My advice is to get it checked out.
I am aware of Seborrheic Keratosis although I know that they are more common in older individuals. I am currently 26 years old and it appeared a year or two ago.
It is worth you getting it checked out by the doctor.
As it is also bothering and feels tender, it may be worth asking your doctor if you can have it removed, especially if you are catching it with your comb or hairbrush.
If the doctor has any suspicion that this needs further investigation, he will refer you to a dermatologist.
Seborrheic keratosis. Not serious but get it confirmed by doc.