Question 1206462
.


The notice "Both seem to work." in the post by @josgarithmetic is INCORRECT.


Only the solution "Gary is 4 years old; grandpa is 60 years old" really works,
since the other solution contradicts to the condition 

    "Today, grandpa's age in years is an even number". 


Based on this my correction, you may get the right final answer on your own.
</pre>