It's a very common question actually.

I think we need to find our own balance between staying "with" a lesson and moving on to new material or songs so we stay interested. 

I find that taking a short break from something I am working on does me a lot of good. I go back to it when I feel I am ready to tackle it again. 

You look about my age. This is supposed to be fun at our age. 

Good luck 

Edit: don't look for perfection. Do the best you can and realize there will be material that fits you better. After 6 years of learning guitar, the right place for me is a nice slow blues. Easy and relaxed.