In the Istock model release the date under "photographer Name" and under the "Witness name" and under de "models name" is:

The model, photographer and witness date of birth or the date when it was taken???

(I supose it is the date of birth but I prefer to be sure before I submit the photo)

Date of Birth is listed under the model.  The others are the date it was signed.

If I remember its's the date you signed the release, there is also a "Date of Shoot" under photographer and a "Date of Birth" for a minor (under 18).

david