nicola horlick , 54 , raised six children while working in the city .
she wants daughters alice , 26 , serena , 24 and antonia , 18 , to go through motherhood earlier .
fund manager says she felt a noticeable difference in her body between her first child at age 25 and her last at 38 .
adds ` ambitious and intelligent ' women should n't be stay-at-home mothers .