Jerry Clark - born May 1962? 1963? 1964?

My brother and I are looking for our half brother. We have differing information about him. According to our aunt, he was born in May, 1964. His name was Jerry and our mother, Carolyn, kept him until he was about 2 years old. Or so we were told by our aunt. She gave my brother 2 pictures of him as a baby. She said that he was adopted by a lawyer in Dubuque, Iowa. I THINK she said he was born at Iowa Lutheran in Des Moines. ???? My MOTHER told me that she was 20 when she was pregnant, that he was in a foster home for about 6 months before her TPR and that it was right before she met our dad. Based on that scenario, it would put his birth in 1962 and at least 4 years old when he was adopted. Also, she said he was adopted to a large farming family in Dubuque, IA. We know nothing about the birth father. Our mother is deceased and we want to find Jerry. Any information would be helpful.