1. Some 51% of young women would have surgery to improve their looks

have surgery to improve their looks
通过手术来改善容貌

2. mostly aged 17 to 34
年龄大部分在17岁到34岁之间。

aged表示“年龄在…岁的”

例如：They've got one daughter, Isabel, aged 3.
他们有一个3岁的女儿，伊莎贝尔。

The elder one is a boy aged 7 and the younger one is a girl aged 3.
大的是个儿子，7岁。小的是个女儿，3岁。

Prisoners aged under 21 are detained separately from adult prisoners.
在惩教机构内，21岁以下的犯人是与成年犯人分开服刑的。