Is the hospital discriminating against older employees?

That they cut hours relative to a pay scale alone wouldn't be the basis for a claim of age discrimination, and in fact the employer would likely use the pay scale/wage basis as underlying their decision - i.e., that they didn't just cut the pay of 50+ year old workers, but all workers in a given salary range to save funds. Of course, you could argue that they used the salary range criteria just because it included all of the workers over 50, but that's a bit of a tough sell to a jury. That said, though, that doesn't necessarily mean that the decision isn't illegal discrimination.