a good site that gives you questions that could be considered comparable to what is on the exam is jbtestprep. If you can get passing grades on that site, you should be able to easily pass the national exam. It is a pay site (around 35 bucks) and the questions aren't exactly like the nremt...
As far as physical demands, it depends greatly on typical volume of calls, type of calls, and crew size. Unfortunately I know a number of fairly overweight people in EMS in my area, and somehow they survive. Biggest concern IMHO is cardio training and core strength. But depending on your...
I have a number of good friends that are 60+ in the field, most are with volly services unless they are medics, and most have 20+ years of experience. In general I would rather run with an 'older' crew than a bunch of youngsters since I have found that there are less egos involved the older we get.