I'm not sure I completely understand the issue. You may offer a discounted rate on a loan so long as it doesn't apply only to (or against) a protected class.
The problems a few years ago involved seniors deposit accounts that came with a loan discount. The age requirement to qualify for that account dropped to 50 or 55 in many cases. You can't "discriminate" based on that age. While age can be a factor, that is eligable only at 62 or older.
Opinions stated are not necessarily that of my employer.