Mexican Fenders are generally pretty good instruments; some are really great; some are dogs. I had a '91 MIM Jazz that was a dog, but I had a '92 MIM Precision that was a fantastic bass. One of the guys in my band has a '92 MIM Jazz and it is one of the best Jazz Basses I've played.
There are a couple things to watch out for---on both of my basses, the nuts split under the G strings, and on my Precision and my friend's Jazz, the pots got scratchy. But, (a) no need to fix it if it ain't broke, and (b) neither of those issues are deal-breakers on an otherwise good instrument. (Not to me, anyway.)
If your son likes it, I wouldn't worry about it at all.
TalkBass: Where all the women are strong, all the men are good-looking, and all the 70s Fenders are above average.
My band: Dec8de
(80s alternative covers)