The breathing sounds pretty normal. Even some of my adults still do that. It just simply shows a bit of surprise, when i. e. they first wake up when I remove the hide.
As to age: Looks to me to be a spring 2007, which would put it at between 5 and 8 months.
Food-wise: Can you get your hands on rat fuzzies? Your BP is big enough to step up and rats provide more nutrition. Another reason for rats over mice: Eventually you'll have to feed several mice in one session and some BP's will not strike and eat multiple times.
Btw, your BP looks gorgeous!