#The Boys Age

The first girl was just 638 days old
The boy twice as much, namely 1,276 days
The next day the youngest girl will be 639 days old
New recruit 1,915 days, total, 2,554 days, which doubles that of the first boy, who having gained one day, will be 1,277 days old.
The next day the boy, being 1,278 days old, brings his big brother, who is 3,834 days old, so their combined ages amount to 5,112 days
Which is just twice the ages of the girls, who will now be 640 and 1,916, or 2,556.

The next day, the girls gaining one day each
Represent 2,558 days, which added to 7,670 days of the last recruit
brings up their sum total to 10,228 days. 
Which is just twice that of the two boys, with the two points added for the last day, would be increased to 5,114 days.


7,670 days by saying, the young lady having reached her twenty-first birthday.
21 times 365 equals 7,665 plus 4 days for four leap years, and the extra one day.
Comes with the twenty-first birthday ,which is one day towards the twenty second birthday.