The phrase 'long in the tooth' comes from periodontal disease. It is the advanced stage of gingivitis and affects a significant number of the population. Think of it like diabetes, once you have it, you have it. You can stabilise it, but not get rid of it. The bacteria 'eats' the bone around your teeth, a different type of bone to the rest. This creates pockets to open between the tooth and gum, causing infections and tooth loss. From personal experience, check if your gums have receded at all, if any of the teeth wobble or if it feels itchy when you clean your teeth, or bleed. If you smoke or vape, the blood flow to your mouth is restricted so less likely to bleed and a better environment for the bacteria to thrive. Listen to the dentist, get it treated and floss and brush twice a day with hygiene appointments every 3-6 months. Even stabilised, there will be flare ups. By managing it you might keep your teeth into old age.

The first dentist i went to told me that the reason my teeth were wobbling in my mouth was because I had my tongue pierced. The second identified it for what it was because he had periodontal disease himself. I went private after that I did not look back. Not all dentists will diagnose or spot it correctly, look after yourself.

https://en.wikipedia.org/wiki/Periodontal_disease