First time ever, I am replying to a thread without reading all the posts. I have lived this with my DH. His mom died when he was a child. DH was 42 when his father died. Right after his father died, a family member told DH he had been adopted! He had no idea. But adoption papers proved it to be true. DH was born in another state but adopted here.
He found this out almost 20 years ago & has never had a desire to try & find biological family. He considers his parents as his real parents. We did discuss it very briefly when he first found out, but it was never a serious thought. But I can tell you, it was a real gut punch when we found out. My DH was a secure, stable adult who was able to handle it. This type of revelation could really throw anyone for a loop.
Even after living they this with DH, I can't say if it is better to find out earlier or later in life. But I can say, he would have been absolutely fine with never having been told this information. If he had a choice, he would have chosen not to know. Tread very carefully.