Do you recommend a 3D Printer for a 13 Year Old

[mechadense]

If he has been wanting one for a year now, then he's most probably really interested.

Using e.g. openSCAD as modelling 3D modelling language
teaches geometry math and programming in a playful manner.

I'd avoid a rather closed system like the cube printer. See here:
http://betabeat.com/2012/05/maker-mo...ng-cartridges/

Being able to improve the printer is part of the fun.
Makerbot & Ultimaker have the gratest US & EU community respectively since they're the ones longest around.
There are plenty of upgrades and accessoires for those printers on the Thingiverse website already.
Don't worry the DIY printer sets are really easy to assemble.