I guess there isn't one clear correct answer... But they say that the loss that causes the most emotional pain is the loss of a child. I'm not a mother so I wouldn't know, but it might be because our dna has programmed us to care for our offspring in order to reproduce, setting aside how many people aren't good at fulfilling the parental role. Society also deems loss of a young life more tragic than the loss of someone in their 40s or 60s. Another factor might be that old age, while already miserable, is even worse to deal with if there is no one to help you or to keep you company. As one reaches old age, they can't spend time with their friends like they could in their younger years, and since their parents are most likely dead by this point, the only ones left to care about them is their offspring. Though I guess there is also an option of a nursery home, but a lot of elderly people can't afford that.
In conclusion, old age without anyone to help is a nightmare, and the emotional pain of that loss is too much to bear. But in my opinion any loss of a loved one is unbearable, no matter the age of the deceased.