You want to estimate the sample standard deviation so you can get an idea of how large of a sample you need.

The topic of your research is "average age of students at community colleges". You assume that the ages of community college students is approximately normally distributed.

Estimate a range of ages that contain the middle 95% of community college students.

Your estimate for the high value of ages for the middle 95% is

Your estimate for the low value of ages for the middle 95% is

Use your range to estimate the standard deviation of the age of community college students.

Use your estimate for the standard deviation to determine the sample size needed to be 95% sure that the average age of all community college students is within 0.5 years of the true average age of all community college students.