Im not religious either so i guess thats really a decision you have to make as to whether to have Santa around during your christmas, just acknowledge his there or not at all.
I took Jesse for his first Santa photo as i wanted him to have it for later on to look back at his first Christmas, so if your question is your DD is too young, not at all. I love Christmas, its my favourite time of year.. a time when families get together and give so much more than just presents and now i have a little one its going to make it all even more special