Several statistical methods for estimating the mean age to reach a milestone were compared using the status quo data on age at menarche in schoolgirls in Shimane prefecture. The material was collected in February 1977 ; it consisted of a random sample numbering 2431 girls aged 130 to 190 months. The records were classified into 3-month and one year age ranges. The standard probit and logit methods were applied to the former classified data to estimate parameters of the frequency distribution of age at menarche. Tocher's grouped probit and its approximation methods were applied to the latter classified data for the same purpose. The estimated mean ages were standard probit 12.562, standard logt 12.554, Tocher's grouped probit 12.564, and its approximation 12.560 years. The mean age 12.580 was also obtained by Spearman-Karber method from the former classified data. No great discrepancy in the estimated mean ages of menarche was noted for any method of analysis. The method determining the age per cent menstruating curve from the individual records that some girls had reached menarche whil eothers have not reached menarche yet was tried to get the mean age of menarche in a small sample of girls. This method could be used to estimate the mean age, if a set of small sample of girls covers enough range of ages, such that in the younger age group none of the girls has experienced menarche while in the older group all the girls have passed their menarche.