Pet age field

For the pet age I would like the field to allow manual input or drop-down calendar selector.
It is impossible to add so many 0yr. 0mo.; 0yr. 1mo. >>> up to 10ys or 12 yr age values in the taxonomies list.

Can I add manual input for this field (or any field?)?

Thanks!

http://wordpress.org/plugins/pet-manager/