It's just the emblem of the publisher. The publishers business name is 'Puffin books' - so they chose a symbol of a puffin bird as an easily recognisable emblem.
I don't think Puffin is looking for quantity of age as much as quality of books. If you are a minor, you will probably need some parental consent form signed.
Puffins like to be near the sea, preferably on an open, grassy cliff-top where they can dig their nests. (Yes, dig.) They're found in the north atlantic/arctic ocean. I recently went to see a colony...