Legal age for marriage

According to Hindu Marriage Act the minimum age for a groom should be 21 and for bride should be 18. A couple who had married before the completion of this age can stay together but if no one would be there for obeject it. 

Kindly clear your question wheather you are asking about the marriage which are hidden from the parents or the marriage has been decided with the wishes of parents??

Is it same for the muslims?...... if yes and they marry before that age in that case who all have the right to object???