21 for males and 18 for females. If any partner(s) engages in marriage at a younger age, (s)he can ask for the marriage to be declared void / annulled. A recent recommendation by the Law Commission aims to equalize the marriage age for males and females to 18, automatically declares marriages under 16 as "null and void", while marriages at the age of 16 or 17 are "voidable..
Whether it will be seen as an issue in the show is matter of W & W..Mostly likely there will be a flying mention of it..whether it will be the crux of the issue, probably not because 3 main issues arises, age, bigamy and human selling..Human selling has been overlooked by the CVs so far but as this is a serial all issues have to be taken with a pinch of salt because dealing with them has not been a strong suit for the show!!