depends on the variety. Some varieties will throw 2-meter canes in the first summer and the next summer the obelisk will be almost covered. But on average it takes around 3 years for the rose to grow high enough. Remember roses don't climb on their own, they just grow long stems that you need to tie into the structure.
This past fall i planted a very young climber (10 inches tall from soil). should i prune it in the spring and if so how much? all the branches/canes are green and the size of coctail staws.