When you are first starting, my opinion is that 13 to 20 knots is perfect.
Any less and you are schlogging. It takes some skill to milk light wind. For a new rider, it can be a nightmare (it's possible, just not ideal).

More is up to the individual (and many might feel otherwise in terms of newbies) but I think 20 plus is where stuff happens fast and you can get hurt.
Probably best to wait at least 5 full outtings before going out in 20 plus.
I am talking local conditions. Some places have no options but to teach in 30, and as a rider you may not have much choice either. Around here, we can get 13 to 20, quite a bit (percentage wise of days riding... not absolute days/year).
I am talking ideal though, and that's not always possible. The fact is, the less days per year of any wind, the less picky you can/will be.