How to find the oldest instances on the heap using OQL

I'm trying to identify a memory leak using visualvm. I found some candidates by comapring snapshots, but since there are too many of these, I would like to narrow the search by locating the oldest instances开发者_如何学编程 on the heap. Is there a way using OQL to search for such instances? I did some googling, but didn't find any answer. This is lead me to a second question - is there a good reference to OQL?

Thanks.

---

1. There is no way to know the age of the instance. Such information is not available in the heapdump.
2. OQL help is available here: http://visualvm.java.net/oqlhelp.html