Is he too young to know

My son is 14 and me and my husband adopted him at birth. His biological mother is my an old friend of mine. She passed away over a decade. Her story is honestly really sad. My son has been asking why he was giving up for adoption. He says he loves us and wouldn't trade us as parents. He's just curious as to why. My friend was being raped and molested by her dad while she was living there because she lost her job and apartment with no where to go and she fell pregnant. She wanted an abortion, but her mom manipulated her into continuing the pregnancy. Last minute, like her last month she asked if me and my husband would adopt her baby. We got lawyers and stuff involved and we agreed. After we adopted him she left the state to start over. A year and a half later she committed suicide. Its such a sad terrible situation. It's a rape, incest, suicide story and I think 14 is too young to learn about it. He doesn't know he is an incest or a rape baby. He is a bit delayed and I think that's a result of the incest rape, but he knows nothing at all. We ended up moving to my husband's home state when he was a toddler to start fresh so he wouldn't be around that horrible family who is the reason my friend is gone. I know he deserves to know about his biological mom and biological dad, but I just think 14 is too young. He has other mental issues too and I know he wants to know but be honest, do you think it's best to wait for this story?