There is no "level" it is a scale. If you fly 120k a year, then you are more frequent than someone who flies 50k and less than someone who flies 200k.

People taking 2 flights a year are more frequent flyers than most of the existing population, in fact, even 1 flight a year may qualify as higher than the median in most countries.

Then, "frequent" flying means something different to you, to an airline, and to your friends and family. I take over 200 flights per year, with a mix of about 30-40% long haul and 60-70% short and medium haul, which feels quite a lot in terms of tiredness and for people around me, but then I once met a guy who was flying one stop IAD-TLV and back every weekend in F, which of course dwarfs my own value to airlines, especially as he was doing his trip always on the same airline while my flying takes me over at least 20 different airlines (let's say about 40-50% OW, 20% ST, 10% *A and 20-30% others including low cost).

So in short it is all relative. With your flying rhythm, at the Christmas dinner table, most people will assume that you fly more than pilots themselves (a joke people often make with me, even cabin crew), while on Flyertalk, you will be considered "small fish" by most, who may well reach your annual mileage by early March.