Interesting. In that article it mentions Sandin is the second youngest player in the Leafs' system after Robertson. I didn't realize he was that young. Almost doubled Liljegren's scoring.
I think you might have misread that section. Sandin (3/7/00) is the next oldest player after Semyon Der-Arguchintsev (9/15/00). Robertson (9/11/01) is nearly a full year younger than Der-Arguchintsev (4 days short).
In ascending order of age:
Nick Robertson
Mike Koster
Mikhail Abramov
Kalle Loponen
Mikko Kokkonen
Semyon Der-Arguchintsev
Rasmus Sandin
Riley Stotts
Filip Kral
Nick Abruzzese
Timothy Liljegren
Ryan O'Connell
Pontus Holmberg
This
https://pick224.com site that Katya linked is super useful for quickly grabbing all the Toronto drafted players not yet in an upper pro-league (NHL, KHL, SEL, Liiga, etc.)