Answer
The actual mean is more accurate, and a bit less than the one we've calculated.
Work Step by Step
The mean can be counted by summing all the data and dividing it by the number of data. Also, at each age group we take the mid range of the group to calculate. The mid ranges: 50-59:54.5, 60-69:64.5, 70-79:74.5, 80-89:84.5, 90-99:94.5, 100-109:104.5, 110-119:114.5, 120-129:124.5. The mean: $\frac{54.5\cdot4+64.5\cdot10+74.5\cdot25+84.5\cdot43+94.5\cdot26+104.5\cdot8+114.5\cdot3+124.5\cdot2}{121}=84.67$. The actual mean is more accurate, and a bit less than the one we've calculated.