OP I made the mistake of setting various targets for myself by the age of 30. it was a very depressing time of my life as while I was pleased with my career etc I had no partner, family of my own etc.
I think life is all about balance and at various times in our lives that balance is out of kilter. Somehow this feels worse if it coincides with a "landmark" birthday.
All I can say is life does change. And if you feel really down for a prolonged period do speak to your GP. Sometimes there are issues from your early life which take on greater significance as you mature
All I can advise is don't push your feelings to one side, seek help. Don't do what I did and resist. I did finally seek help from my GP who was unexpectedl kind and understanding.