is it true that if a person could travel at light speed, she would age differently from a regular person on earth? If so, how/what would make that happen?
In essence, yes. What you’re describing is an important element of special relativity. I’ll explain below.
We know that the speed of light is constant in any reference frame - no matter what speed you travel at, you will always observe the speed of light to be 3.00x108 m/s. Period. Since any observer will always see light traveling at this speed, it is impossible to travel at or faster than light.
So knowing this, what happens if I’m traveling at 90% the speed of light in one direction, and you are stationary? I’m going to observe light moving at 3.00x108 m/s, but so are you! Now, if I’m going at 90% the speed of light and time flows the same for me as it does for you, won’t I observe light traveling at 190% the speed you observe? Based on what we know already, this cannot happen, since that would lead to two different measurements of the speed of light, and impossibility.
In order for both of our measurements to be the same, time and space have to be different - time has to slow down for me, and my length has to shrink relative to yours, since velocity is a measure of distance over time. So you would observe me being shorter, and time flowing slower for me (so I would be moving in slow motion). However, from my perspective I am not moving, and you are moving at 90% the speed of light in the opposite direction. I observe time flowing slower for you, and I observe your length as shorter. Both observations are equally accurate, and there’s no way to prove which one is accurate - if we were to take videos of each other passing by, my video would show time flowing slower for you, and your video would show time flowing slower for me, and both are equally accurate. So yeah, that’s the basics of special relativity for you. Pretty wild, right?
Here are some resources that should help out as well, along with providing some more in-depth details that weren’t covered here; I would DEFINITELY recommend watching the two videos below. I also included graphs of time dilation, which shows how time is impacted by speed, and length contraction, which shows how length changes based on velocity.
TL;DR time and length have to be relative in order for the speed of light to be constant in all frames of reference. Thanks for asking, and I hope this was informative. If I went too in depth // any of it went over anyone’s head, feel free to ask me questions about it! I love answering them. Sorry this is so long, but it was the only way to explain this well.