My grandmother said that when she got older, she stopped getting bitten by mosquitoes. However, the itching and swelling that occur when bitten are actually allergic (immune) reactions to mosquito saliva. As people age, these immune responses tend to become slower and weaker. In addition, aging dulls the skin’s sensory receptors, making it harder to feel itching or pain. Furthermore, older adults often have difficulty hearing high-pitched sounds such as mosquito wingbeats, and presbyopia (age-related farsightedness) makes it harder to see mosquitoes, reducing the likelihood of noticing them nearby.
It is not that they are bitten less often: older people are still bitten by mosquitoes just as much. The symptoms simply appear less noticeably or with a delay: due to changes in immune response and sensation, itching and swelling occur more slowly and mildly, making it easy to mistakenly believe they haven’t been bitten.