1a] He broke the fast deliberately when he was younger; what should he do?

1a] "And whoever transgresses the limits ordained by Allah, then such
are the Zalimoon (wrong-doers, etc.)"
[al-Baqarah 2:229].
And just as if he did this act of worship before the time for it
began, it wouldnot be accepted from him,by the same token if he does
it after the time for it has ended it will not be accepted from him
unless he had an excuse.
End quote from Majmoo' Fataawa ash-Shaykh Ibn 'Uthaymeen, 19/89
In the case that it is obligatory to make it up, if the individual has
forgotten the number of days on which he broke the fast during
Ramadan, then he must do what he thinks is most likely to be the case,
because Allah, may He be exalted, says (interpretation of the
meaning): "So keep your duty to Allah and fear Himas much as you can"
[at-Taghaabun 64:16]. If he thinks it most likely that he broke the
fast on ten days, then he should make up those ten days.
And Allah knows best.