Question 1046130
The mean of the sample means for all sample of size 40 will be 24 years old.  The mean doesn't change.
The standard deviation does change, and it is sigma/sqrt (40), the sample size
That here is 2.5/sqrt (40)=0.395
The z value would be (xbar-mean)/0.395=-1/0.395  or 1/0.395
The z value is between + and - 2.523.
The probability it will be in that range is 0.9886 (rounding may change the final digit).  That means that a single person may have a significant probability of being distant form the mean, but as you group people together, the average of all of them is much less likely to be.