Is it true all body cells replace themselves every seven years?

Answer 1

different cells have different lifespans, most will take less than 7 years, for example red blood cells have a limited life span of around 100 to 120 days and must therefore be continuously replaced.

Answer 2

No. If all body cells replaced themselves every seven years then our bodies would never age (grow old). But our bodies do age, which means that many cells continue to die off without ever being replaced.