* Constellations are patterns of stars: They are made up of stars that are at vastly different distances from Earth. The stars themselves are very old, but the specific pattern we see as a constellation is just a perspective from our planet.
* Stars are constantly moving: Even though we see them as fixed, stars are actually moving through space, and these motions are slow but measurable over very long time scales. This means the pattern of stars we see as Leo will change over millions of years.
So, what's the age of the stars in Leo? The stars in Leo are billions of years old, like most of the stars in our Milky Way galaxy.
The concept of "age" for constellations is more about how long they've been recognized by humans. The constellation Leo has been recognized for thousands of years, and it's mentioned in ancient Babylonian and Egyptian texts.
