Draft was started in 69, with the first lottery draftees in 1970 (I know this fact with 100% certainty). Bush went into the Guard in 67 and one could claim he did it in anticipation of being drafted.
Bush went into the Guard right after graduation in 1968, the Draft was started in around 1966 but the Lottery system came in in late 1969. Remember Clinton was able to stall things until this lottery system came in and he got a high number so that he knew he would not be drafted.
Bush enlisted into the Guard in 1968