It is not permissible to have a birthday party for anyone, as it constitutes a Bid`ah (innovation in religion). It is authentically reported that the Messenger (peace be upon him) said:
Anyone who introduces anything into this matter of ours (Islam) that is not part of it will have it rejected.
This is also done in imitation of the Kafirs, and the Prophet (peace be upon him) said:
Anyone who imitates a people is one of them.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family and Companions.