30... hmmmm.... I think I can remember being 30...
Well, as some people say, getting old is a bear, but it beats the alternative. (A a Christian you have to question that assumption, but you get my point.) I think that all young people look at older peopole and wonder why on earth they chose to be old instead of choosing to be young.
The longer you live, the more you can have learned (It isn't automatic... you have to pay attention and work at it some.) and more you have to share with others and help other people. Many things improve over time - sex with one's spouse, for one, one's appreciation of almost everything, your sense of history, you usually become more patient, there are more people in you life who you love and who can love you. And believe it or not, one can still be active and healthy and enjoy living for several decades after turning 30.
I think you need to readjust your image of the various ages. You have probably bought into the youth culture, which is so very prevelent, which tells us that only that which is young is good and beautiful and anything old is undesirable and unattractive. As you have discovered, it is an inevitable journey. You can't refuse to take it, but you can control you attitude about it. You need to learn to love the age you are.
In your 30s you are still a young person.