dragon ballz was the first ever anime that i watched it is still one of the most popular anime yet. any kid would love too watch it and imagine that they are a sayian and they have these awesome powerups by screaming and energy blast. the only reason that older people are watching it because most of them have been watching since they were a kid with wild imagination and they have grown to love the character and they like to keep up with the story line.
but a grownup who has started watching would not like as much as if they had seen is as a kid. Dragon ball franchise lacks a sophisticated story line, it is all about screaming, power-up and endless fighting. just look at the naruto franchise for a moment i think it is superior to dragon ball z in many ways like its has sophisticated background, ancient storyline and how it links to the present events, diffrent people with many diffrent power traits, not only that but the Naruto franchise also reflects on the real world aspects such endless wars, pain, misery and suffering also the happiness prosperity in life.