Testes not showing up could be many things... some boys drop late, or never drop them. It seems to be more common now than it used to be (It's genetic). Also, stress, illness, and enviromental change can also cause them to bring them up for protection. Also if it's cold they will brng them up. And, at that age they are still covered in fur, so not as visible.
He looks in THAT pic around 9 weeks... based on the face, and headshape. He LOOKS like he's getting his adult coat, has lost the "baby face" and is in an akward adolesent stage. It's not the greatest pic though.
And so you know, a BOUGHT rat, is never a 'rescue'. If you buy a rat from a retail establishment you didn't 'rescue' anything, except the store that made an easy buck, and will be bringing in more rats to replace him since they obviously sell.