What is the idea of Islam about underage marriage for women? Is it true that a 9 years old girl can get married with a 60 years old man by her father or grand father advocacy? Is there any Islamic rule to stop people who force their underaged daughters to marry?
Forced marriage of any kind is forbidden in Islam. It does not matter if the man/woman is 9 or 18.
Ibn Abbas reported that a girl came to the Messenger of Allah, and she reported that her father had forced her to marry without her consent. The Messenger of God gave her the choice...(between accepting the marriage or invalidating it) (Ahmad, Hadith no. 2469).
another version of the report states that
“the girl said: ‘Actually, I accept this marriage, but I wanted to let women know that parents have no right to force a husband on them.’” (Ibn-Majah).
The only restriction regarding age is that both persons be sexually and mentally mature. For some this can be earlier than 16 and for others it can be later.
"Is it true that a 9 years old girl can get married with a 60 years old man by her father or grand father advocacy?" - yes, but only if the girl agrees and is not forced, and with other islamic requirements of marriage. if she shies she can show agreement with silence.
"Is there any Islamic rule to stop people who force their underaged daughters to marry?" - yes: there are hadithes that strictly say that her consent/acceptance/permission is mandatory: http://sunnah.com/muslim/16/80 http://sunnah.com/bukhari/67/72 http://sunnah.com/tirmidhi/11/28