I seem to inhale/exhale once every 2 seconds on average myself. 5 seconds is a freaking long time per breathe. Now if your running or exerting yourself you will actually inhale/exhale almost every second, but if your sleeping etc, it might be a bit more then every 2 seconds. I just made the average one per 2 seconds though, so 30 per minute. Drastically changes the number in my calculation though.
Maybe your right. I was relaxed when I tried counting so I was breathing slower. Also, only 78M breaths? I know you're older than I am, but you have less than half of what I got. And if you're counting every 2 seconds you should have even more. One of our maths must be off.