It has only been in the last ten years that America recognized dual citizenship, if he became an Indonesia citizen prior to that say like in 1965 or when ever he moved there and his adopted father made him an Indonesian citizen, he lost his natural born status because he became the citizen of another country.
In that case even if he went though the process to re-establish his US citizenship at 18 (and there are no records of him doing so according to the rules of the State department) he would only be a naturalized citizen and eligible for the presidency.
not eligible for the presidency.
I don't know who told you this, but it's not the least bit true. Read the case law. Try Afroyim v. Rusk for starters:
The fundamental issue before this Court ... is whether Congress can consistently with the Fourteenth Amendment enact a law stripping an American of his citizenship which he has never voluntarily renounced or given up.-snip-
[The Fourteenth Amendment] provides its own constitutional rule in language calculated completely to control the status of citizenship: "All persons born or naturalized in the United States . . . are citizens of the United States . . . ." There is no indication in these words of a fleeting citizenship, good at the moment it is acquired but subject to destruction by the Government at any time. Rather the Amendment can most reasonably be read as defining a citizenship which a citizen keeps unless he voluntarily relinquishes it. Once acquired, this Fourteenth Amendment citizenship was not to be shifted, canceled, or diluted at the will of the Federal Government, the States, or any other governmental unit.
-snip-
We hold that the Fourteenth Amendment was designed to, and does, protect every citizen of this Nation against a congressional forcible destruction of his citizenship, whatever his creed, color, or race. Our holding does no more than to give to this citizen that which is his own, a constitutional right to remain a citizen in a free country unless he voluntarily relinquishes that citizenship.