It would be easier to tell with a picture, but I am guessing sunburn. When moving a succulent outside it needs to be acclimated to the intensity of the sun. A few hours per day then out into the sun. If the plant has not been repotted for a long time, I suggest you also do that. Wash all of the old dirt off the roots and use a good potting soil mixed 50/50 with a coarse grit (I like hadite). Give it a good drink and move into *partial shade* or *morning sun/afternoon shade* for a week or two. When it is fully acclimated you can move it into full sun and it will be quite happy, rewarding you with lovely red margins. hth -
Jo

Donna, if it was wild, was it not growing outdoors?
I'm missing something..LOL
Are you watering too much by chance? Yellow leaves usually indicate overwatering, but can also mean underwatering too.
You also mentioned u haven't repotted in yrs,..perhaps it's so rootbound that's why plant stoppded growing??? Toni