The main character of the Catastrophe short story (in the collection Short Stories by Munshi Premchand) was descried as "an old, childless widow" who "didn't own either a scrap of land or a house to live in." However, it's later stated that "She had spent her fifty miserable years in this village and she loved every leaf on every tree. Here she had known the sorrows and pleasures of life; she could not give it up now in the last day." Why was 50 seen as being old and towards the end of someone's life? What was the life expectancy in that area at the time?
The simple answer is this link to a chart of life expectancy in India over time.
As you can see, life expectancy was around 20-25 for the entire period of Premchand's life. It is likely that expectancy is lower than the average in rural areas, where the story is set. That's less than one third of life expectancy today, and half that of Europe at the same time.
The character has already lived twice as long as average, and so is old.
While I give the simple statistics, in reality things are slightly more complicated. Life expectancy can be skewed by large numbers of infant deaths - for example if 90% of infants die at birth and the rest live to be 100, the life expectancy is still 10 years. Someone who survived to adulthood could reasonably expect to live to be older than 25. However I do believe that 50 is older than most people live to in 1900s India, especially in a rural area with hard work, little healthcare and most women having their first of many babies while still teenagers. 50 is probably past what most adults survive to.
While another answer had addressed statistical matters of overall life expectancy at birth, with a presumption of that rural areas having and expectancy below average, I think there are other things to consider more particular to the character in question.
Premchand does not say that fifty is old, per se, he says that this woman is old at fifty.
What do we know about her? That she lives in a village owned and governed by a man who has little regard for the welfare of its inhabitants. We might assume that this individual has not been in control for all of her life, but also there is no reason to suppose that he runs the place any differently from perhaps his father before him. Therefore it is plausible that this woman has spend her whole life, or at least her whole widowhood, regularly expected to work for no income, and for that work to prevent her carrying out the work that brings her food. A life of malnutrition is ageing.
While the parching of grain does not itself sound like the hardest of physical labour, we see that when the kiln is destroyed she begins to rebuild it herself, suggesting that such labour is not foreign to her. If the parching only brings in a subsistence level of food, she may have had to hire out her labour to neighbours to allow her to earn other necessities of life, or a little cash to buy them.
Childbirth is a leading cause of female mortality, more so in deprived regions. That hasn't affected Bhungi, we might speculate that poor nutrition may have contributed to her childlessness, and the lack of children has meant that there are no other hands to contribute to her sustenance. She may have had little respite from work in her adult years.
A person in his or her 40s who lives in or near poverty has a level of biological risk similar to that of a person about 60 in a better-off family.
It is not to be supposed that a female relative of the village landowner would be so worn down by work and depleted by poor nutrition.
Premchand was particularly concerned with the realities of life for impoverished peasants, per wikipedia:
In the 1920s, he was influenced by Mahatma Gandhi's non-co-operation movement and the accompanying struggle for social reform. During this period, his works dealt with the social issues such as poverty, zamindari exploitation (Premashram, 1922), dowry system (Nirmala, 1925), educational reform and political oppression (Karmabhoomi, 1931). Premchand was focused on the economic liberalisation of the peasantry and the working class, and was opposed to the rapid industrialisation, which he felt would hurt the interests of the peasants and lead to oppression of the workers.
The references in the wikipedia article about the explotiation of peasants by the Zamindari is relevant to this question as well as your questions about ownership of a village and Bhungi's poverty. I went down quite a rabbit hole of trying to distinguish what state land ownership and was at in Uttar Pradesh at the time of the story to try for some answers, but very quickly realised that that is quite a specialised subject and difficult to get a handle on from a standing start. However Zamindaris were landowning aristocrats who were co-opted by British Rule as revenue collectors for their estates.
Whether the rural poor have a lower life expectancy than the urban poor, I don't have figures to discuss, though the wikipedia article certainly suggested that Premchand himself thought that rapid industrialisation, which would lead to increased urbanisation of the poor, would be detrimental to the condition of the peasantry.
Bhungi isn't old at fifty 'because India', she is old at fifty 'because poverty'.