Mass and speed both slow down time due to a phenomenon called Time dilation.
Time dilation can be explained by Einstein’s equation as below:-
If we travel for 14 years at 99% of the speed of light (nearly 14 light years distance), it will be equal to 99 earth years as explained below:-
The gravitational time dilation equation is given by:-
Below video explains time dilation due to mass i.e gravity
When we move at 99% the speed of light or orbit a highly massive object like a black hole which warps the fabric of space time, it causes the time to slow down, the rate of which is shown above.
These laws of physics apply to all types of matter including biological matter at cellular level and thus, the biological clock slows down as well.
Photo credit: NASA
This is the reason why aging slows down when we experience time dilation either due to speed or gravity which is a by product of mass.
Same is seen in the Hollywood Sci-Fi movie Interstellar.