Actually, no. I think Elton was a big selfish self-involved baby himself until relatively recently. He has more or less said this about himself in interviews over the years. Surely it's good that he didn't go down that route until he gained 'maturity' himself?
I just see two really happy people thrilled to bits with late fatherhood.
Who can ever forget Tantrums & Tiaras when Elton was playing tennis, someone called out to him and he had a hissy fit, packed up and went home? That isn't a person who sounds ready to become a parent. Time changes and matures people, and now he feels ready to become a parent.
And good luck to him. It's obvious he and David adore Zachary.