I'm 20 now but I picked my lip for about three years in high school and stopped when I was probably close to 18 (It was something fun to do during school). For at least a year, It must have went on longer than that but I haven't noticed, there's been a callus over the top of my bottem lip and over most of the middle. It's horrible because it covers so much of my lip. It looks like a scab, and maybe it is a scab. It never, ever heals or goes away. If I try to let it heal it gets moist and eventually just falls off by itself and then a new scab or callus grows. Sometimes I just bite it off when it's become a bit detached from my lip because theres no reason in letting it stay there to heal. It's awful because I know that every time it falls a harder callus is growing in and it may never heal. When I put lip chap on it it gets moist and falls off.
I suppose what I could try is to put lipchap on it, let it fall off, and then put lipchap on all day long so that the callus is always flattened to the lip from the beggining and never has a chance to get spiky and detach.