One way to determine your intensity is to rate how hard you feel you are working?

Yes and how hard you feel about the specific topic in general

for question 8

1: it gets the blood pumping more

2: endorphins and other neurotransmitters

age might have something to do with behavior depending on the age because not everyone who is the same age acts the same like 2 year olds could have bad behavior but some won't.

i hope this : )