According to the principles of special relativity, time dilation occurs when an object moves at speeds close to the speed of light. This phenomenon means that time is experienced differently for observers in relative motion.
In the scenario you described, if you were to travel away from Earth in a spaceship at speeds close to the speed of light and then return, you would indeed experience time dilation. However, it's important to note that reaching the speed of light is not currently achievable for massive objects according to our current understanding of physics. Nonetheless, let's consider the scenario hypothetically.
From your perspective aboard the spaceship, time would pass slower for you compared to your friends who remained on Earth. This is due to the time dilation effect caused by your high velocity relative to them. As a result, when you return to Earth after 5 years of your subjective experience, you would still be 20 years old.
From the perspective of your friends who stayed on Earth, however, time would have passed normally for them. They would have experienced the full 50-year span, so they would indeed be 65 years old when you return.
This phenomenon is a consequence of the principles of relativity and time dilation. While it may seem counterintuitive, it has been experimentally confirmed through various observations and measurements. However, it's important to reiterate that achieving speeds close to the speed of light for massive objects like humans is not currently within our technological capabilities.