I totally agree with everything Mike B just said. The key is finding what you like.
In general, the strong aroma of many oolongs will begin to dissipate with age. Since I love the scent of fresh oolong, I generally find that oolongs over a few years old aren't as satisfying to me. So I tend to drink greener oolongs soon after harvest and darker ones 6-18 months later. But that's just me. Many folks will say that any loss in aroma in an older oolong is compensated by additional complexity in mouth-feel, etc. I'm drinking a batch of 2007 Thief Poop right now, and it's very good.
Really old oolongs, say 1970s and before, often have a strong taste and smell of camphor. To me, this is interesting to try at least once, but I wouldn't choose to drink it more than rarely.
Good luck exploring!