The thing with shonen is that it can be defined as a genre. We can say "targeted at young males", but what does that actually mean? It tends to mean a focus on action, the plot usually driven through repeated conflict resolved through battle of some kind, and it tends to have an absence of romance or only uses it as a comedic plot element (One Piece being a great, long running example of all of the above). Granted, not all shonen will necessarily stick to these basic guidelines, but I could rattle off about a dozen more prominent shonen anime that follow them practically to the letter.
I mean, you can't say that shonen has a target audience and then say that there are no genre specific trends of appealing to a specific target audience. That literally makes no sense.
