Is it a good idea to repeat full body mri after lets say every 1 to 2 yrs to pick up any small tumors (god forbids)after age 50 or so?

Probably not.: Unless you are particularly at risk, the chance of a false positive result will substantially outweigh the chance of a true positive result(i.e. an actual abnormality). The follow up medical testing will never end. There is no evidence I know of that suggests that routine whole body MRI would be a net benefit.

No: Doing tests or imaging studies without a specific indication is a bad idea. It is not only wasteful, it may lead additional tests, surgeries and complications due to a some innocuous finding from an unneeded investigation. 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.