Soaps always play games with the characters' ages, the SORAS routine, and DS is really no exception. David Selby was 29 in 1970 but he is established as the father of 14 year old Daniel, if the character's age is in synch with David Henesy. There's less of a glitch with Lara Parker who was about 32 at the time and had two sons who were close in age to Henesy.
In the 1840 sequence, a few months later, when Selby is playing another Quentin who is the father of Tad, the character is a bit older, 32.