Filming for the first Star Wars movie began in 1976. The actors weren't kids back then, so they've certainly aged a lot in the intervening 39 years. Now, in The Force Awakens, Luke, Han, Leia, Lando, and Chewbacca have new challenges, such as mobility, endocrine health, and diminished mental acuity.
In this great sketch from Saturday Night Live (content warning: foul language), you can see how well the actors have held up. No one is going to jump around a sail barge anymore without breaking a hip in the process.
The scene with Leia trying to figure out R2-D2's controls is perfect.