B12/folate are high. MMA is low norm. Vegan, haven't supplemented for yrs. Dr. says my current B12 store can last 6+ yrs-life with no more supp. True?

Take supplement. Without knowing how long you will live, I would not make the statement that B12 reserves are good for life. As a vegan, it would be safer to take B12 and Vitamin D3 supplements.
For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form.
Practice safe sex, if you have sex.
Get HPV vaccine, if you are under 27 years of age.
Probably true. . Vitamin B12 is stored in the fat tissue of the body. So you can develop quite a storage of B12, and other fat soluble vitamins, and they’ll leach it of the fat tissues slowly for years. I don’t know if you’re supply will literally last all of your life, but it’ll last. Periodic monitoring given your vegan diet would be fine (1-2x/year).