I have a Toyota T-100 that I have had for about six months and it has about 211,500 miles on it, with no major replacements or accidents and all original parts, but I am nervous that it may not last too much longer. Around what mileage will it start to break down or will it maintain it self if I keep up with its routine check ups?

do regular oil changes and check ups it will run forever

Toyota typically are high mileage vehicles. They had like 11 of the highest mileage vehicles last year i believe (consumer reports or something). But im not so familliar with the trucks. So im not exactly sure if they run up as high (400k+). Any individual vehicle can vary. But if it has no known problems it should be ok for awhile.. at least i feel that. Even my Chevy s-10 lasted to like 225k

I would think at the mileage you are at you will only see small problems like the alternator/battery, A/C system, Alignment/suspension bushings, maybe a fuel filter or pump.

I think you will be OK to about 275,000 or 300,000 before you should have it thoroughly looked over.