Praise be to Allah.
Death is a great calamity and trial, with which a person’s good deeds and lifespan come to an end, and the individual goes to meet his Lord. If he did good then the outcome will be good, and if he did evil than the outcome will be bad. Death causes tears to flow, saddens the heart and provokes grief.
Allah, may He be exalted, says (interpretation of the meaning): “And certainly, We shall test you with something of fear, hunger, loss of wealth, lives and fruits, but give glad tidings to As-Sabirin (the patient ones, etc.)” [al-Baqarah 2:155]. Loss of lives is included among the calamities that may befall people.
And Allah knows best.
All of this has to do with general guidelines. With regard to what is mentioned in the question, about the death of elderly people being a cause for calamity to befall the family, or a cause of a decrease in barakah, this is something for which there is no evidence whatsoever. People older and younger are constantly dying; if the death of an elderly person was a cause for a decrease in barakah or of calamity occurring, barakah would have been erased in this world and one calamity after another would have befallen the members of every household. But this is contrary to what is seen and known, and it is different from the way in which Allah has ordained things should occur in this world. How many elderly people have died, yet their families enjoyed blessing after they were gone, either because of wealth that was left to them or because of a blessing that was bestowed upon them, or because of a woman getting married and other things that are seen and well-known.
Moreover, what connection do the living have with the death of the elderly person, such that calamity as mentioned by this questioner would befall them, regardless of whether the deceased was righteous or otherwise? Allah, may He be exalted, says (interpretation of the meaning):
“Whoever goes right, then he goes right only for the benefit of his own self. And whoever goes astray, then he goes astray to his own loss. No one laden with burdens can bear another’s burden”
Rather real calamity befalls people with the death of a scholar of whose knowledge the people are now deprived, or one who was devoted to worship and obedience, or one who did things that bring benefit to people, such as striving in jihad for the sake of Allah, enjoining what is good, forbidding what is evil, giving charity and zakaah, and so on. All of that has nothing to do with whether a person is young or old; rather it has to do with how he is, the benefits he brings to people, and the blessings he brings to his surroundings. Undoubtedly the death of such people is a loss of goodness and barakah, and detracts from people’s religious and worldly interests. Those who are most sorely affected by their loss are those who are close to them, but this does not mean that another calamity will befall them after that, unless they do after that an action that deserves that. It was narrated that ‘Abdullah ibn ‘Amr ibn al-‘Aas said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “Allah will not take away knowledge by snatching it away from the people, rather He will take away knowledge by taking away the scholars until, when there is no scholar left, people will turn to ignorant leaders who will be asked questions and will issue fatwas without knowledge. They will go astray and lead others astray.” Narrated by al-Bukhaari (100) and Muslim (2673)
And Allah knows best.