I feel like the best description of the timeframe is not the years that you've been drawing because people tend to consider a year as drawn even if they only draw as a hobby, on weekends, such that the actual base of work doesn't add up much. While I can't concretly say how much work you put in, there is a rule of thumb for "mastery", or rather achieved skill: 10 000 hours. That's ten thousand hours of PRACTICE! It's a huuuuuuge investment. Now even before that you'll likely be above average in your chosen skill, but a rule of thumb to think when you're likely to have "learned" drawing is that. That's a ton, and that 10 000 hours is grueling, boring study work (anatomy, perspective, composition, boxes, value, forshortening, boxes, boxes, and more boxes), but it's what's necessary. I'm not even close, but I also don't claim that I'm learning much, I do this for self expression mostly.