How many 85 year olds...

[prohornblower]

I think my answer lies somewhere between 100-300.

Pushing them over and tripping them would yield great results while expending little energy.

I think I'd be able to keep going until my fists went numb, or I passed out from hunger or thirst. The thought of this is quite disturbing.

I think if you make the age 100, I could take all of them. All of them on the planet, with little effort.

70 year olds would yield a much, much lower number. Maybe like 20. Chr*st, Jack Nicholson is 70, to put it in perspective. I don't think he goes down too easily.