Suppose for a minute that you as an 18 year old want to earn a living as an electrician. You have studied electronics all your life, played around with wiring, etc. and you are better at wiring schematics than any other 18 year-old, or even 25 year-old electrician for that matter. The only problem is: all of the construction firms, builders, maintenance companies, etc. that hire electricians are required to deal only with certified, union electricians and you don't have your union card. Furthermore, to get a union card requires a two-year apprenticeship and then a one-year internship, so you can't get a job as a fully certified electrician for three years. It has nothing to do with your rights and has everything to do with entry requirements.
As long as he passes the physical and drug tests just like any other athlete..
AND as long as he meets the eligibility requirement of THREE YEARS OUT OF HIGH SCHOOL "julst like any other athlete."