Although young adults are generally healthy, by their early 20s, a natural physical decline brought about by increasing age, has already begun

Senescence

Explanation:

Senescence is defined as the gradual decline of functional characteristics. It can either be a senescence of the whole organism of just cellular senescence. In this process, cells stop dividing and just enters into permanent growth arrest stage without the cell actually dying. It can be caused by unrepaired DNA damage, increasing age, or other stresses to our cells.

precisely the author keeps the interest of readers not describing clearly the   kind of relationship in giselle's family. by doing this, readers had to imagine and assume how it was.   instead, the author described better scenes with dark star and the influence of books about horses in giselle's life and actions.   also the fact that she broke her arm but not referring to it in detail leads the readers to imagine and guess what could have occurred.