A man can have sexual pleasure from a child as young as a baby. However he should not penetrate, sodomising the child is OK. If the man penetrates and damages the child then he should be responsible for her subsistence all her life. This girl, however does not count as one of his four permanent wives. The man will not be eligible to marry the girls sister.
From Khomeini's book, "Tahrirolvasyleh", fourth volume, Darol Elm, Gom,
Iran, 1990
It is better for a girl to marry in such a time when she would begin menstruation at her husband's house rather than her father's home. Any father marrying his daughter so young will have a permanent place in heaven.

From Khomeini's book, "Tahrirolvasyleh", fourth volume, Darol Elm, Gom,
Iran, 199