To be more explicit: What is needed to make the statement interestingly wrong is for the two 20-year figures to be in different reference frames. If your twin does something for 20 years, then they will be 20 years older; but if they do something for what you experience as 20 years they may not be.
To be more explicit: What is needed to make the statement interestingly wrong is for the two 20-year figures to be in different reference frames. If your twin does something for 20 years, then they will be 20 years older; but if they do something for what you experience as 20 years they may not be.
Edited to more firmly attach “for 20 years” to the earth.