The numbers on the teats refer to the number of holes, not the age.

Number 1 - 1 hole, for newborns
Number 2 - 2 holes, for 1m+
Number 3 - 3 holes, for 3m+
Number 4 - 4 holes, for 6m+

And then the variable flow one doesn't have a number, just the different groups of lines to align with the baby's nose.

BW