That depends...are there still any activities you can enjoy even if only briefly?
Do you ever still feel motivated to do anything? Are you ever not lethargic?
While apparent loss of the brain's local reward-system is the simplest sign of Major Depressive Disorder, chronic irritability and displeasure are also probable red flags.
If, within the last three months, you can still function normally a decent amount of the time, then you're probably still in the clear.
Of course, if you're convinced there's a significant underlying problem, then you should probably get professional help regardless of what I just said.
Going back to the original question, Major Depressive Disorder is probably not something any age-group should be expected to have, but I'm not sure if that's what you meant by depression in the first place...