I guess that would depend on the tree, wouldn't it? How is a tiny little seedling going to clean as much carbon as a tree that took 40 years to become anything substantial?
Well... the process of that seedling growing into the big tree over 40 years is what takes carbon out of the atmosphere. The carbon just goes into the tree's biomass. So - long term, if you have a steady state where the biomass of the trees you're talking about remains roughly constant (or dips but comes back to the same level) - it is carbon neutral. Even if you're cutting down big trees and planting seedlings.
Of course, you're right, there's nuance there. If you start with a mature forest, cut it all down, and replant it with seedlings, that's not a steady state (yet) - particularly when you take ecosystem effects into account, I suspect.
If you take land that doesn't currently have trees on it, and plant a bunch of trees that you periodically cut down and replant then you're at worst carbon neutral. Unless that land would have otherwise be planted and left alone entirely.