Simplify the following text for a Grade 7 native English-speaking person.
Original: Girls usually complete puberty by ages 15 â `` 17 , while boys usually complete puberty by ages 16 â `` 18 .
Simplified: The changes in a girl 's body during puberty usually take place between the ages of eight and 18 years . Most girls will have finished puberty around the age of 15 .