I have about 50 songs and 6 instrumentals in my head that I can do to a performance standard. I generally do not forget lyrics. What I do forget is - what songs I know, key, capo position, starting chord shape and sometimes tuning. I keep a list of of songs with that info on my computer, phone, and kindle as well as hard copy in the guitar case printed in a large font. I still learn a new song every month or so but it takes a while (3 months?) before it gets added to the list of things I can actually do. I also regularly forget where I put my car keys, wallet etc.