Thanks for your input, inquest. The examples you cite all relate to some objective criteria concerning the law's applicability. Driving and child labor laws are based upon attainment of a certain age as indicative of physical ability and responsibility. The same with airman's certificates and physical performance standards for positions in public safety occupations. What the author is questioning here is the relation ship based rates which are discriminatory along the same lines as would be the case if tax rates were age or race based.
I know I'm walking into a mine field, but this is a real sticking point for me. The 14th amendment makes no distinction between race-based, age-based, relationship-based, or ability-based criteria. It also contains no escape clause for "compelling state interest", in the words of that thoroughly obnoxious phrase that judges love to use (and which in my opinion should be viewed as them signing their own impeachment warrants): Either it's prohibited or it's not prohibited, regardless of how "legitimate" the reason might seem.
I don't mean to be harping on you at all, it's just the system that I'm frustrated with. I have a real problem with judges who make up the law as it feels convenient to them.