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As per the law, mandatory birth registration is there. But even now, the coverage is low in the rural areas. And you can imagine the situation we had 15 or 20 years back, when the data was not stored digitally. A lot many times, the compiled data would be lost (either due to natural disasters such as flood, or due to accidents such as fire). And the penalty given to the offenders is not very serious and it actually encourages such crime. For example, Delhi player Prince Ram Niwas Yadav was found to have faked his age in a domestic U-19 tournament two months back. He was only given a two-year suspension (BCCI could have banned him for life). In his case, he was 24 year old but claimed that he was 19 so that he could participate in the U19 tournament.
After the implementation of Adhar card Indo not think it is easy for anyone to manipulate Birth date in India. If I am correct the government does verify all the details submitted in Adhard card with the central database.
Every Gram panchayat and local municipal corporation are issuing Birth certificate. 15 years ago it was a completely different thing. It is very hard now to fake Birth certificate, after the digitalization of data done by UID.