Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
age group n возрастна́я гру́ппа
the forty to fifty age group лю́ди во́зрастом от сорока́ до пяти́десяти лет
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.