Great article!
Interestingly we are born with some “old” things, like senescent cells 
As Groucho Marx once said “I was born at a very young age”
I don’t think there are that many senescent cells in children. Scarring shows the presence of senescent cells.
Senescent cells are created, even without “damage” that could cause scarring.
“Zombies” Stimulate Stem Cells Shortly After Birth
Using this highly sensitive tool, the researchers found that senescent cells exist in young and healthy tissues to a greater extent than previously thought, and actually begin appearing shortly after birth. The scientists also identified specific growth factors that senescent cells secrete to stimulate stem cells to grow and repair tissues. Relevant to aging and tissue injury is the discovery that cells of the immune system such as macrophages and monocytes can activate senescent cells, suggesting that inflammation seen in aged or damaged tissue is a critical modifier of senescent cell activity and regeneration.