I love this idea! It'd add a very nice looking leaf block (great texture btw) and make for some more biome variety.
I have three suggestions though:
Have fewer leaves per bamboo. I think with how many leaves you have, the canopy seems much denser than it should be. I think just a thin layer of leaves per bamboo would he fine.
Put the leaves higher up. Somewhat goes with my first suggestion, but having them extend so low makes the biome feel cramped.
Use a different biome name. This is more personal taste, but I'm not a huge fan of the old growth motif, and I don't think the name rlly fits as much here. "Leafy bamboo forest" would be perfectly fine and easy to remember.