20 lessons a day sounds like a good pace to me. Some people learn differently than others.
I’ve been at it for shoot, possibly close to 3 years now, and I’m only level 16. Life happens too.
However, if you’re going to continue at that pace, (and it’s comfortable), I’d recommend getting Lifetime to save yourself some cash - if you have that much upfront, anyway.
You may want to spend more time on your lessons before you do the final quiz at the end of them - this will slow your lessons down but hopefully make them stick better when it comes up during your reviews.
We’re cheering for you!