It's not "age discrimination" (in the negative-connotation sense), it's sober rational thinking.
"By 38 you can't take so many risks-- especially if you have kids" is a statement of fact.
"This is one reason I'd bet on the 25 year old over the 32 year old." is a reasonable conclusion.
Calling this age discrimination is like saying all employers are evil because they discriminate based on having or not having skills required for a job.
Even if we suppose it were "sober rational thinking" that doesn't mean it's also not a "negative-connotation". Fifty years ago a southern business would have been engaged in "sober rational thinking" to deny service to blacks or at worst to make sure they were "properly" segregated.
In more modern times a more apt comparison would be with respect to pregnant women. Suppose he'd written instead "This is one reason I'd take the childless, single 25 year old woman over the married 32 year old. By 33 she'll probably be pregnant or have a baby."
That's very clearly discrimination, and very clearly in the negative-connotation sense.
For similar reasons, PG's statements re: age are very clearly "negative-connotation" age discrimination. Moreover, there's nothing particularly "sober" or even "rational" about it, considering the heaps of evidence regarding age and people who are very successful in running businesses (hint: "young" isn't exactly a word that comes to mind).
"By 38 you can't take so many risks-- especially if you have kids" is a statement of fact.
"This is one reason I'd bet on the 25 year old over the 32 year old." is a reasonable conclusion.
Calling this age discrimination is like saying all employers are evil because they discriminate based on having or not having skills required for a job.