The X Factor is a book .
Following bootcamp , successful acts were split into four categories : Boys -LRB- male soloists aged 16 to 28 -RRB- , Girls -LRB- female soloists aged 16 to 28 -RRB- , Over 28s -LRB- soloists aged 29 and over -RRB- and Groups .
The X Factor -LRB-UK series 7-RRB-