You need to tell us the temperature in the enclosure as well, because if it is too hot, he will roam around the cage and try to get as far away as possible from the heat lamp.
My veiled is 7-8 months old and he did the exact same thing as yours is doing at the same age, this is a time in their lives when they really try to determine their own territory, so he is probably just doing that.
If it isn't that, then it is the size of the enclosure.
That enclosure can be big enough depending on the size of the animal, but i would say the miminum for a sub-adult male veiled is 24x24x48". The problem is probably a combo of the two of these things.
My guy grew out of that activity a month or two ao and is quite happy perching all day long on the upper branches now, and he does't claw at the cage.
Try to find/build a new cage for him ASAP becaue he is probably uncomfortable in that size of a cage.
Look on www.adcham.com for some cage designs you can use.