I couldn't open your capx cause I use the stable version of construct but I have a simple solution.
You use every X seconds, all you have to do is using a variable as X.
For example, if X=(yearsVariable/10) then every (10/10) 1 seconds
when he is 20 years old ---------- every (20/10) 2 seconds
If it's too quick, create timespeedVariable and use it as X.
Every timespeedVariable seconds
You change timespeedVariable when he is 20 years old.