With an ADN/RN, he can work as a nurse, even though some jobs do prefer BSN. This can allow gaining some nursing experience and getting a feel of what nursing is like before committing to a post-high-school educational path, in addition to earning some money to pay for future school.
Also note that if he completes the ADN/RN by high school graduation, he would have the option of applying to most colleges as a frosh if he decides to switch to something else instead of doing an RN->BSN program. However, if he does switch to something else, note that ADN/RN course work may not be applicable to some other paths (e.g. pre-med science requirements).
The other thing to consider is that regular BSN programs tend to be highly competitive for admission (either frosh direct admit or secondary admission). Direct admit programs may also have high GPA weed-out policies. It is definitely a riskier path to BSN than the two-step of ADN/RN first followed by RN->BSN.