Average age of mairrage is very high in Urban areas and a little less in rural areas but still way higher than 18 both including men and exclusively women as well.
Not to mention average gets low because of muslim community which has lower Mean Age of mairrage.
National average of women who were married by the time they became 17 was 27% back in 2020 and it goes down evey year by 4 to 5%.
India national average was never 18 even a decade or two ago.