lovefaith
May I suggest posting this question in the Depression Forum.
There is no certain age where depression manifests itself to the best of my knowledge. It can strike anyone at anytime. Children as young as 3 years old have been dx with depression. If you wonder how a 3 year old is noted to have depression, a loss of interest in play appears to be a red flag that a child between the ages of 3 and 6 is depressed.
Please do look at talking with the members of the depression forum if you feel you are depressed.
Anxiety and depression often go together.
Take care,
Kitt