Should I offer our younger, healthier employees a higher salary since they don't utilize their healthcare benefits too much?
The goal of insurance is for the "risk" to be spread across the entire group. You cannot decide that different types of people (age and health) must pay different premiums.
Some companies now offer employees reduced health insurance premiums if they do not smoke or stop smoking, live a healthy lifestyle (as determined by set criteria) or who join weight loss programs.
However, these must be well-devised programs put together by experts and be administered very carefully to ensure fair-handed treatment.
Age and health, in general, cannot be used as a criteria for how much anyone pays for his/her health insurance in a company's group plan.