Excess Life Tax Calculation

Hello,

We are having the discussion of the interpretation of the IRS publication 15b in regard to what age do you use for the excess life tax.  The IRS says use the employees age on the last day of the employee's tax year.  So for this year would we look at how old they will be on 12/31/2018 or 12/31/2017?  For supplemental life we use the age as of Jan 1st to calculate premiums but for the tax my co-workers are saying to use end of 2018.  So they have the age range in the calculation table moved up a year