I'm not aware of any research on this specifically.
But there is research on the average age of sexual debut, and the average age of first marriage, and you can use these numbers to make a educated guess.
In India, the average age of sexual debut is approximately 22.9 years, while the average age at first marriage is 24.1 years
It's probably a safe bet that most people have sex shortly after their marriage (if not before), and therefore that even if NOBODY had sex before marriage that the average age of debut would not be higher than marriage + 6 months.
What we can't know is if these numbers mean that only 2% of Indians wait until marriage with having sex while 98% have their debut at age 15 or something; or conversely if this means that 100% of all Indians have their debut in the last couple years before marriage.
Thus this can't be anything more than a guess. Here's my guess:
It's relatively rare for Indians to have sex as teenagers, certainly only a minority does, and probably more than 80% or something like that does.
It's common for Indians to does not wait with sex until at least close to the marriage.
An example distribution that is possible, and would match the data I mention at the start is this one:
2% of Indians wait until marriage with sex, and when they marry they have sex within the first month. 99% of Indians have sex before they marry; on the average these start having sex 2-3 years before they marry.
Please note that this is merely a guess that would fit the available data; it seems more or less plausible but I have no idea if it's actually a correct guess !
Written By Ravi Vaghasiya