There is no statutory rule to this effect. What exists is a judicial tendency, applied on the facts, which is a very different thing from a right.
What the law actually says
The Hindu Minority and Guardianship Act, 1956 provides that custody of a minor who has not completed five years shall ordinarily be with the mother. Beyond that age, the statute gives no preference by the child's gender at all. The Guardians and Wards Act, 1890 directs the court to the welfare of the minor as the paramount consideration.
Why courts often still place daughters with mothers
Judges frequently take the view that a girl approaching or in adolescence benefits from the mother's presence for reasons of care, guidance and privacy. That reasoning is common and it is often decisive, but it is applied as a factor. Where the mother is unable to provide a stable home, or where the child expresses a settled contrary preference, custody has gone to fathers.
There is no fixed age at which a child's preference becomes decisive, but courts routinely interact with children in chambers and give increasing weight to the wishes of a child mature enough to form an intelligent preference. Judges are also experienced at spotting a coached child, and coaching backfires.
What actually moves the decision
- Continuity: schooling, home, friendships, and who has been the day-to-day carer
- The practical realities of each parent's working life and support network
- The willingness of each parent to preserve the child's relationship with the other
- Any documented issue of safety, substance abuse or neglect
Custody is not all or nothing
Even where physical custody goes to one parent, the other ordinarily receives structured visitation and retains a say in major decisions, and joint custody arrangements are increasingly ordered where both parents live in the same city and can co-operate.