They say a gas type star is 5-10 million years old.
Nope. The object, K2-33b is vastly older than K2-33. I think I should hit up MS paint again to give the appropriate placement of the two objects. Look down around where Neptune is on the graph, that's where the ancient star is K2-33b. The young hot star, K2-33 is right where the yellow stars are most likely.
I've also read the article. They don't mention how old the host star is. Plus there is no link to the paper published in Nature. We're just suppose to "trust them" I suppose. Little known fact, to them all host stars are the same age as their adopted partners. This is just plain inaccurate and invalid according to stellar metamorphosis.