To find source data quicker, use a Google Translated version (Google Chrome can do this) of the EStats Japan dashboard website following the dataset below and Ctrl+F for 'Births' while on 'All'
日付
原典
投稿者自身による著作物, data was taken from the EStats Japan Dashboard using 'Population/Household' dataset of 'Number of births to X age group (9 data slots from under 15 to over 50)'