What are the causes of gum disease if elderly?

Follow below. The same criteria would apply to you as with someone half your age. We would still review your medical history, check your medications, illnesses, habits, genetics etc... Treatment can vary and might include laser therapy which is very effective and relatively conservative.
Age. As we all get older, the effects of even a small amount of gum disease over our lives, compounds. The rate of bone and tissue loss from gum disease varies from individual to individual. Our bodies evolved to survive for around 50 years . After 50 years, hard and soft tissues can fail at a faster rate. Thankfully, there are many new and effective ways to treat tooth and gum loss.
Age/hygiene. Habits like brushing agressively, not brushing at all, not flossing, not getting regular cleanings, smoking, some medications, and to a very small extent bone diseases. Most are completely preventable with good oral hygiene and routine dental check ups.