How can you tell if a doctor is incompetent?
Age isn't an indicator here.
And no, it's not easier to figure out your own ailments. It's much easier to find flaws in other people's judgments.
Let's say I go to a doctor, tell him all this. And he says: "Well, what are you making up? Everything is fine with you. Get a girlfriend, get an interesting job, find a hobby, do some sports, spend less time on the computer, go to discos, and everything will be fine. Here's a prescription for vitamin C. Goodbye! Next!"