[SJackson]

My guess is that it's something "new age."

Nope, you're wrong, custom dates to BC in the English calender, not AD.

[zook]

What I thought we were referring to is the practice of writing "God" this way in modern English text. What was done 2000 years ago isn't relevant to the question of why it is I, as a reasonably well read person, did not encounter this practice until quite recently. I grabbed the term "new age" in a generic sense, meaning a desire to return to and restore some ancient understanding.