There's been a great deal of research lately on the efficacy of flu shots, and also why some people seem so resistant to getting sick without protection. As it turns out, older people don't get as large a boost from the vaccine, but they usually do get some – IF they contract one of the three viruses included in that year's shot, they will generally have a milder/shorter course of illness.
This has been my experience – the years I've gotten the shot, I either have not gotten the flu at all, or have had one or two relatively mild illnesses that were more than likely the common cold.
It's also been learned just recently that a significant number of people have a natural, secondary means of fighting infection built into their immune systems – those blessed with this hereditary factor are the people (who perhaps include your family) who seem to never get the flu or colds.
Stomach "bugs" are not the flu, even though they are often called that.
However, real influenza is a potentially serious, and often deeply miserable illness that attacks the respiratory system, and the producers of the vaccines do their best to guess which of the many strains of virus are most likely to cause the biggest outbreaks in any coming year, so people will get the most protection possible. That does NOT include all of the potential viruses that can cause an outbreak, so it is still possible to catch one of the "off brands" in any given year. And occasionally a non-included virus turns out to be a bigger problem than anticipated. Even the most educated guesses sometimes go wrong.
If illness occurs shortly after receiving a shot, it's common to blame the shot. But those are not caused by the dead viruses included in the vaccine, UNLESS the person was exposed to that particular live virus just before or shortly after receiving the shot, before it has a chance to trigger the immune response. It generally takes about two weeks for full protection to build. The dead virus in the vaccine can NOT cause the illness.
Flu can be deadly for seniors and very young children, and for those with lung problems, diabetes, or compromised immune systems, and there are always some people who cannot be given vaccines at all. So improving "herd" immunity helps reduce their risk, even if the shots don't do a perfect job of protecting every recipient. The shots do help significantly reduce the impact of an outbreak.
Just for a little perspective, during the great flu outbreak of 1918, when my grandmother was a child, there were no vaccines available. My grandmother lived in Chicago, where thousands of people in surrounding neighborhoods died over just a few weeks, including her own parents and baby sister. That was a hard, sad thing for her to live with – I think she grieved about it for the rest of her life. She remembered her helplessness when her baby sister was dying, and the terrible fear of not knowing who would be struck next. She and her two surviving sisters were left to raise each other to adulthood, because too many members of the extended family had died to take them in.