@bluebayou, @astrotemp
Thanks for the advice, guys.
The ball is already rolling, all applications are in. I checked on the MathematicsGRE website - it seems that most of the posters there don’t have publications, while my son does. His rec letters - coming from three different Universities and one from industry, from his co-authors and his teaching professor. His co-authors I am sure addressed his maturity, which, as you can imagine, is not necessarily a linear function of age. His lowest ranked “safety school” is ranked #44, the rest are above 40. His research boss (who did write recommendation letter) doesn’t have any doubt he will get into several of his targets. His professor at the home BA-degree university thinks he will get into more than half. They all know his age, and the difference between his recommenders and you guys is that they actually have met him and worked with him or taught him. Whose opinion do you think is closer to the truth, I am wondering. 
Let’s see how it all pans out.
As for the age preference or absence thereof… I had several conversation on the subject with a friend of mine, who used to be in the graduate school admissions committee in a school ranked in top 35. (He is not participating any more). He told me that when they worked on assessment of applications, they cared about ability to do research, and to teach. Age was not the thing they ever hanged their decisions on.