Not that it's conclusive proof against his claim, but my wife and half her immediate family members have the same birth date as this guy (month, not year, obviously). The other half have the 1st of July.
They just didn't bother remembering "irrelevant" details in the villages, so whenever it was that they first signed up for an official document of some sort, they were just assigned one of those 2 dates.
The head of the village will basically confirm and sign anything as long as it's reasonable. Just so people can go ahead with their lives. Everything would grind to a halt if they all had to do things by the book.
I was 40 when I married my wife and my father in law was 42 but over the years the age gap between us has steadily increased to the extent that I am now 54 and my father in law is 60.
Again, not conclusive proof against this guys claim but Indonesians seem to just think of a number if they don't really know.
Time seems to be something that they can't grasp the subject of.
As regards to the head of the village signing anything so people can continue with their lives, the kepala desa wrote a letter saying that my wife's 2nd husband had died about 4 months after my step daughter was born so that my wife would have no impediment to marrying me.
In fact they'd just split up and the fact that he'd never sent money or letters was enough for the kepala desa to accept that they had divorced but thought that death would make sure that there were no more questions. I have never met him but he still lives in Central Sulawesi somewhere.
Off topic a bit but related to time, when I was younger I cycled from England down to Cape Town, also using boats and planes on a couple of occasions, e.g. Cairo to Nairobi because Sudan, as it was then, especially southern Sudan was a no-go area.
Quite often if I asked someone has far it was to the next village or town they would reply that it was 3 cigarettes or 2 cigarettes so they measured how long it would take to get there by how many cigarettes they would smoke on their journey.
The only problem with this was I didn't know if they smoked 5 a day or were a chain smoker so it didn't really help very much