Hello! The meaning of "rudeness" is the quality of being offensive or not polite. and The meaning of "insolence" is rude and disrespectful behavior. So the official meanings of these words are similar, but I would say that in everyday English "insolence" would be a better word to describe the behavior of a child or young person that is rude or disrespectful. and "rudeness" would be a better word to describe the behavior of an adult who is being offensive or impolite. I hope that helps!

(American version) Rudeness = any type of bad manners Insolence = disrespecting your boss or someone in a "higher" position. The official explanation may be different, but this is how I think of these concepts.