How many miles can a 2003 toyota celica clutch handle before being replaced?

It really depends on your driving style and where you live. In San Francisco, I have seen clutches go in less than a year. You live in Colorado, but how is flat is your area? Also, if you drive your vehicle in a high performance way and don't put in the trans in neutral at stop lights, it can go out in 1-2 years or sooner. If you are conservative with your clutch and the parts on the replacement clutch are factory quality and there is no oil leaking on to the disc from the rear main seal and valve cover gasket, it can last 100,000 miles or more. This is why dealerships won't warranty a clutch for more than about 30 days. It is because people drive clutches in a wide variety of ways. I actually witnessed a Subaru owner ruin a brand new factory clutch in 2 days, because the driver did not know how to properly drive the vehicle.

1 to 5 years and 20,000 to 60,000miles or more depending on your driving habits but if your easy on your clutch it will last quite a long time