Islam prescribes fasting for all Muslim adults because it is a religion that wishes for every Muslim to attain spiritual heights and be recipient of the Grace of God. Islam does not desire the practise to become a burden on those who are not able to fast. Thus, those who are incapable of fasting due to sickness or travelling are exempt from fasting in the month of Ramadan and are required to complete the missed fasts later on. Pregnant women, menstruating women, and suckling women are also exempt from fasting. Further concession is made for those Muslims who cannot complete missed fasts later on; hence they are obliged to pay fidya (a compensation for not fasting— feeding the poor and destitute). 

Read more on Fidya here

Fiqh Ahmadiyya: There can be 4 conditions of fasting while on a journey:

If the journey is in progress, whether it be on foot or otherwise, then you should not fast because in this condition leaving the fast is mandatory.

If during a journey one needs to stay somewhere overnight and there is everything available and there is ease, then you are allowed to fast. It is upon you to fast or not. Even if you are staying there the entire day.

If the journey begins after eating Sehri and finishes before the time for Iftaari, or believes that it will end before Iftaari time, then he can fast.

In 1937, the  magazine Al Fazl published a list of 61 weaknesses to work on during Ramadan, written by Hadhrat Mirza Bashir Ahmad (ra).

In his explanatory note, he wrote:

"This year, I again wish to exhort others to adopt that which I have been practicing myself during these past years, namely that during the holy month of Ramadhan members of the community should select one of their own personal weaknesses and make a firm resolution to God Almighty to get rid of it, so that when Ramadan ends, at least one personal weakness has been eliminated."

A list of Ramadan Goals

Hazrat Musleh Mau`ud (ra) has said:

In my opinion, the command for fasting is from 15-18 years of age because this is the age of puberty or maturity. One should practice at the age of 15 and make it mandatory at the age of 18. When we were kids, we used to want to fast, but the Promised Messiahas would stop us. For a child’s health and strength you should stop them from fasting. When they are 15 they should slowly begin fasting and increase gradually.

(Al-Fazl, 11th April 1925)

Here is alislam page on Ramadan FAQ.