The thing is that the age he gives (23) is so low that it's at odds with the principle, the same way as if I said "kids should wait till they're a bit older to

The thing is that the age he gives (23) is so low that it's at odds with the principle, the same way as if I said "kids should wait till they're a bit older to drink alcohol, like after 8 years old" and someone disagreed and said 18 years old is a better age, they wouldn't just be agreeing with the principle and disagreeing with the number.