Here's what ya gotta do.

Do your pushups against stairs.

Place your feet at the bottom, and put your hands on whichever upper step is most comfortable. Because more of your body weight is supported by your feet than is during standard pushups, less stress is put on your arms. I don't know about you, but my elbows act up pretty quickly.

In this position, you'll be able to get a few more reps in which will go a lot farther in conditioning you than 10 - 20 regular pushups at a time will. Once you break 50, then add in some standard pushups and you'll find that they don't wear you out as much. If you're really into experimenting...move your hands around. Closer together works your triceps, farther apart works your chest, and each hand on a different step works your delts.