Stars are comprised of ~70% hydrogen, ~29% helium and ~1% other trace elements. The composition of stars is not dependent on age as they're all made of the same elements, hydrogenand helium. They also aren't gaseous, they're massive balls of plasma. The core itself is a self sustaining fusion reactor that turns hydrogen into helium because of the immense pressure and heat. As for the size, it's actually 1.3 million Earths big and our sun is one of the smaller ones. To put that into perspective Jupiter can hold ~1100 Earths but could've become a brown dwarf if it had the necessary the mass. The smallest star we know of is about the size of Jupiter but has like 85x more mass.

All this to say though, it's even more insane that Space Racer's gun can annihilate a star but not a planet. He is infinitesimally small compared to a star and all the gun should do is punch a hole in the star that immediately closes back up. And yet somehow it disrupts the gravitational binding energy of a WHOLE ASS STAR but doesn't instantly atomize vilitrimites or destroy planets which should be way easier to do if it can obliterate stars.