The PATH you have to add is not /Users/jeong/work/Sage/sage-6.4.1/local/bin, but /Users/jeong/work/Sage/sage-6.4.1/, where the sage script belongs to. Then this script will use what is in /Users/jeong/work/Sage/sage-6.4.1/local/bin.
The PATH you have to add is not /Users/jeong/work/Sage/sage-6.4.1/local/bin, but /Users/jeong/work/Sage/sage-6.4.1/, this is where the sage script belongs to. Then this script will use what is in /Users/jeong/work/Sage/sage-6.4.1/local/bin.