It seems that the 1st got older, like in his 40's, then handed the reigns over to the younger 2nd.

Sarutobi is the last name of the 3rd Hokage. Saru means Monkey in Japanese. That is why Kishimoto named him Sarutobi. Sarutobi Asuma is a relative of the 3rd Hokage, he looks even more like a monkey. We are not sure if Konohamaru is the son of Asuma or what, but he is most likely his nephew, I doubt they are brothers.