MyCup™ Menstrual Cup Size 0 is:

Perfect for first time cup users aged 12-18 years – And if you think a smaller cup might suit your body then age is no restriction!
Suitable for people who may use smaller sized tampons. This is not a strict rule though.

The dimensions of the MyCup™ Teen Menstrual Cup Size 0 are as follows:

Capacity to breathing holes: 16.5 ml
Capacity to rim: 22 ml
Length including stem: 62 mm
Length of cup only: 44.5 mm
Length of stem only: 17.5 mm
Width of diameter: 38mm