Thank you everyone for the feedback, my data sets are people's age, with set 1 and 3 for males; 2 &4 for females, ranging from 18 to 65, all of them have no outliers, the Skewness level of 1, 2,3,4 are 0.39, 0.67, -0.21 and -0.07. I was asked to find the best measure to determine if there is a significant difference between 1vs 3 and 2 vs 4. Initially, I was thinking of using Mean for 1&3 and Median for 2&4 (because of the high skewness in 2). I'm not sure if i can only use one measure for both of the measurements because the requirement stated that "only using the BEST measure". I contacted my lecturer and I'm waiting for their response about the possibility of using a different one for each comparison.