Given SInger's ability to recast characters ( see X2 for that) , i'm all for a teenage jason. As long as he doesn't look too old.
The thing with Routh and Boswourth is that they look very young compared to Christopher Reeve and MArgot Kidder. I could believe those two having a child with the age of Jason in SR.
With SR , it's a stretch since i do know that there are couples who tend to stay young looking for a long time even when they have kids. Other couples grow older a bit.
So that's were the problem lies a bit. They need to make both characters look a bit older IMO. Just cut of the dreamy soft porn filter look that they used for the cinematography and go for wrinkles and stuff. AGE the characters.
And while were at it , why not cast Freddie Highmore who gave a great performance in Charlie and the chocolate factory and Finding Neverland.
Or if they can remove those spots from his face , the kid who played Edmund Pevensie in Narnia , Skandar Keynes
Heck i didn't even know that he bares a good resemblance to routh until i googled that pic .