Typically, unless someone is an absolute mess they are either going to be prone to gum disease, or cavities, but not both (within reason). People who typically build a lot of calculus on their teeth have more mineral content in their saliva and a higher pH environment. This is helpful for remineralizing enamel, but is problematic for health of the gums/bone because it’s impossible to completely clean the surface of calculus, which is essentially hardened biofilm. When you are young, you get away with a lot of habits that you won’t as you age. Flossing and regularly having your teeth cleaned aren’t necessarily critical when you’re a kid, but it will catch up with you in your 40s/50s/60s... it’s a lot like strength training, you don’t ‘have to’ lift weights to be fit in your twenties, but you’ll regret it when you age. When you’re born you look like your parents, when you’re old you look like your choices.