Answered by Shaykh Faraz Rabbani
1) If in the past I intentionally broke my fast by eating food (without any valid reason), but do not recall if I was a child or man at that stage, do I need to make up?
How do you know that you intentionally broke your fast?
If you *do* recall this, then use your reasoned judgment as to whether you were a child or a man, for when certainty is not possible reasoned judgment is used.
2) If I was fasting Ramadan, and washed my mouth and nose during ghusl to such an extent that water went into me, do I need to make up a fast?
You would only have to make up the fast if you are CERTAIN that water entered your body cavity. If you think it MIGHT have, then this doubt is not sufficient to lift the initial presumption of validity.
3) If I need to make an obligatory ghusl during Ramadan how far down my throat do I need to make water go?
Your throat? It is obligatory to wash the mouth. What has the throat got to do with it? In Ramadan, one does not exaggerate, lest water go down the throat.
4) If I never used to always make a specific intention for an obligatory fast for each day of Ramadan, is my fast invalid? If so, do I make up 1 day or 60 days?
If at any time from Maghrib of the night before you had the determination to fast the next day, this is a valid intention, and there is absolutely no need to make up such a fast.
Imam al-Samarqandi mentions in his Multaqat, a book of fatawa, that it is DISLIKED to makeup fasts or prayers for no reason.
5 ) Does rain which falls into my mouth accidentally corrupt my fast?
Nope. Not unless you become certain that it has gone down your throat.
6) Does the following corrupt my fast? If saliva goes onto my lip, and then I take it back into my mouth.
The way to deal with waswasa and misgivings is to read a basic text of fiqh properly with someone qualified and to act on it.