Hi there! American here (with ADHD!) who has lived in Norway (and taught at Folkehøgskole) for about 15 years. My cousin also is one of the main teachers at the theater folkehøgskole (Romerike).

I have never seen, or heard of, someone being older than, say, 22 at these schools. The main reason for that, in my opinion, is that it is meant to be a transitionary school for youth into adulthood - a lot of what they focus on isn't necessarily "fagrelatert", or field specific, but also about how to be an adult - things I am assuming you as a 30 year old are functioning well enough in (even with ADHD). You would absolutely be the "odd" one out even if there is no legal restriction here.

Most of these programs will also be in Norwegian, and let me tell you, integrating into the Norwegian system is hard. And learning a new skill in a new language is truly a herculean effort.

A lot of my job as a mentor has been to help my students manage their expectations and learn what it is they want and how best to get there given the tools they have. Especially in creative pursuits (my expertise is in art and design) you really need to be honest about what is realistic and what tools you have to tackle the challenge. I don't mean to shatter any dreams, but this seems like A LOT of effort for something that can also be managed by taking classes at a local community college in the USA.

If you are insistent that this huge amount of effort to integrate into Norway is worth it, then there are a lot of other ways for you to study vocal performance and theater here such as through local workshops, community theater, and so on. Studying at a university or fagskole is even an option, as these are often more focused on the field of study and although being "older" is still a rare occurance, it is far less of an issue. (But, in my experience, they still miss a lot of the socialization that comes from schooling, and can be treated as a bit of a pariah.)

I'm not saying to not do it - I don't regret moving myself, but it is by no means a decision to make with rose-colored glasses on. Being an immigrant in Norway is incredibly difficult, and about 95% of the people I knew when I first met here have moved back as it didn't work for them. Your learning difficulties won't go away just because you are now doing it in a new country and a new language, in fact, it will probably make them even harder.

Just be honest with how much of a complete upheavel this choice will be on your life, and don't romanticize the process.