Some employers can vary their reimbursement rates by age. Most marketplace plans offer premiums in a 1:3 ratio for individuals ages 26-64.
For example, you could set reimbursement rates for a 26-year-old $100/mo and a 64-year-old $300/mo using the 1:3 ratio. A 37-year-old employee gets whatever amount on the linear line in between the 26 and 64-year-old—Get ready to dust off your old algebra skills! The answer for the 37-year-old in this example is $158/mo.
So what happens if you have a birthday during the year and are now eligible for a higher reimbursement?
The change in allowance does not go into effect until the following year. So if your birthday is in August, you will receive a higher monthly allowance in January of the following year.
Once your insurance ends in December and you sign up for a new plan for the year, you will have a higher reimbursement amount to go towards that premium.