Can a company give special treatment to people on social security?

I was in the office at my apartment building the other day and heard them telling a new tenant that his rent wouldn't be considered late until a week into each month. They have previously made a big deal about how any tenant who turns in rent after the first day would be considered late and immediately served a three day notice and late fees tacked on. I asked them about this, and the office manager told me that they give people on social security special treatment. Is it legal to discriminate between people with disabilities and people without, as long as you're not treating the disabled people worse than the people who aren't?