1. Nope - but diff companies will want different backgrounds. My first content strategy role came after a decade in higher ed.
2. From my experience, not so much (or the pay is very low). If you build a good portfolio of content you've written, ranked + companies you've worked with/for - the # of years really doesn't matter.
3. The advice I got was to hone in on my strengths. You could specialize in a type of content (case studies, interviews, long-form, etc.), the technical side (data analysis, technical SEO), or distribution (partnerships, social media campaigns, link building).
Also, diving into a single industry will help you climb the respective ladder faster. If you already have a background in education or retail for example, aim to land in those types of companies and leverage your existing network.