When I am erect I can only retract my foreskin to just below the glans. When I am flaccid it goes all the way down. Is there a problem and should I do foreskin exercises like you mentioned in other answers? Should it go all the way when erect like it does when flaccid?
While your foreskin should go all the way down, what you describe should not cause you any problems or discomfort when you have sex with your wife. There might be some stretching over time as you have sex, but the position it is in will only cause a gentle stretching.
You can do the stretching exercises if you want, but it is not a critical need. See "I can pull my foreskin right back, but when it is pulled back it is really tight and I don't know if it is normal or if if I need to be circumcised."