Time doesn't slow inside the train. It only slows when you look at the train from outside the train. A mosquito flying inside the train or a passenger moving inside the train appears slower to an observer standing on the ground.
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Your skin is another obvious indicator of your age. This doesn't just include wrinkles, but things like dry skin and tired eyes, which can both be avoided. Reddit user Redhaired103 posted in /r/AskWomen that dark circles, pale skin, puffy eyes, and heavy makeup can also make you look older.
So depending on our position and speed, time can appear to move faster or slower to us relative to others in a different part of space-time. And for astronauts on the International Space Station, that means they get to age just a tiny bit slower than people on Earth. That's because of time-dilation effects.