Who Must Fast Ramadan?
Fasting Ramadan is obligatory upon the person who is:
1– Muslim: A person must be a Muslim or else his good deeds would not be valid and are not accepted by Allah.
On the Day of Judgement, the non-Muslim will be punished for not becoming Muslim and for not performing the obligations, one of which is fasting Ramadan.
2- Pubescent: Islamically, a person becomes pubescent when he or she attains fifteen lunar years of age, or in the case of a male he has had his first ejaculation, and in the case of a female she has had her first menstruation, or has seen her maniyy, whichever comes first.
3- Sane: Fasting Ramadan is not obligatory upon the insane.
4- Able to fast: Any person who would be harmed by fasting due to (e.g.) sickness or old age is not obligated to fast.
In fact, it is sinful to fast when it is harmful to do so.15311:22