Lyrics can be a toughie when playing guitar because you are putting your mind through two processes (or even more, really). So that can be a challenge. I would spend drive time to work etc, hammering down the lyrics to a song or two until you can stop a song and sing any next line. Then is should be easy to remember an play at the same time.
I'm 43 and I remember everything!
Lyrics can be a toughie when playing guitar because.......