Your son may not need to use the entire amount of his tuition, but it is a CRA requirement that any Tuition and Education Amounts are used to reduce his tax payable to Zero.
Tuition amounts reported on a T2202 or equivalent slip must be used to reduce tax payable in the current year. Any credit left over may be either transferred to a parent or spouse or carried forward.
Note that the use of Tuition credit is NOT optional. The software will apply any eligible credit to reduce or eliminate tax payable. Your only choice is to carry forward or transfer and only credit earned in the current tax year can be transferred.
Unused Tuition is tracked by CRA and amounts are reported on your Notice of Assessment.
Amounts may be seen in My Account and are downloadable using AutoFill (AFR).
If you have unused Tuition, you can enter amounts under the Tuition section of 'Deductions' when using TurboTax.
Amounts of unused credit are applied to reduce tax payable automatically. There is no option to voluntarily postpone the use of unused amounts. CRA knows your unused amount of tuition and they will apply the credit even if you do not enter the carry forward amount yourself on your current return.
Here's some more information on Tuition Transfers and CarryForwards from TurboTax: Frequently asked questions about transferring and carrying forward tuition and education amounts
