Sniffles, what a rough time you've had. My aunt adopted their two children and she and my uncle told them when they were quite young and this was a long time ago, so I'm suprised that your parents think you should wait until you're 25 to find out. You have a right to know. Unfortunately, your parents perhaps feel insecure and fear that you will dump them for your biological mother and/or father. Perhaps if you reassure them, they might be more helpful...?
I wish you the very best in finding your biological parents. Even if you never have a relationship with them, it can help to know where you came from. I can understand your wanting to know.
(((sniffles)))