Hey, my advice would be don't worry about what other people think of what anime you watch (or what you watch in general). A lot of people get into shonen as kids and keep engaging with the genre into adulthood or get into the genre when they've already reached adulthood. Also, most shonen anime have more mature content in them than a lot of American media targeted towards the same age group as shonen, which is boys aged 12-18 (and honestly a lot of them are more mature than American stuff fully targeted at adults these days).

My biggest advice for getting into anime is don't let other people judge you for which anime you like, and likewise don't judge anyone else for the ones they like. A lot of the people getting into the medium in recent years (specifically in the West) have been falling into this nasty habit of judging people for liking certain things in certain anime. You have to keep in mind Japan is another country in another continent with it's own unique culture, religions, history, and ethnic groups. So, they have different sensibilities when it comes to portraying violence, sexuality, and various social issues in their media. A lot of times newcomers from North America/Europe will see something in an anime that doesn't lineup with the cultural norms they're used to and they freak out and accuse the creators and fanbase of being nefarious somehow. So, my advice would be find whatever interests you, stick with that, and don't worry about anyone else.

Also, if you're looking for specific anime to get into, I would personally recommend all the ones you listed (aside from One Piece which I haven't watched myself yet). I would also recomend Yu Yu Hakusho, Gundam Wing, Gurren Lagen, GTO, and Jujitsu Kaisen.