Well, in that case
********************SPOILERS BEYOND THIS POINT!!!*************************************
I never really figured out just how an exiled god who had been in our dimension for at least a few centuries, since the Knights of Byzantium (?) had been searching for either her or the Key for at least that long, could coexist with what was obviously a young man (at least there was never any mention of Ben being immortal)
Either he was actually far older than he appeared to be, of Glory somehow managed to shift from one human host to another when the previous one approached death. But if that were really the case, then Giles killing him was an exercise in futility, singe Glory's spirit, soul, or essence would simply move on to another likely host.
I guess that was another one of those things that we were supposed to just accept and not try to analyze.