Using bone meal on kelp cannot grow it past a random length

That's how kelp works, when it's planted it gets a random value that essentially decides how high it can grow.

Thank you for your report!
However, this issue is Working as Intended.

The report you have submitted is working as intended: Kelp plants have a maximum "age" or height of 25 blocks and are assigned a random age when planted or broken. See MCPE-42575.

Please note, that mechanics of the game may change between updates.
Things such as graphics, sounds, world creation, biomes, redstone, villagers, and animals may not work the same in current versions.

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Reopening as this does not match Java Edition.

Hi!

Does this issue still occur on the latest version of the game?
Can you please write repro steps in this format?
Steps to Reproduce:

Observed Results:
(Briefly describe what happens)

Expected Results:
(Briefly describe what should happen)

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Steps to Reproduce:

1. Build a 1 block wide water tower that goes up to the build limit

2. Place kelp at the bottom of the tower

3. Use bone meal on the kelp

Observed Results:
The kelp stops growing at a random height.

Expected Results:
The kelp should grow up to the build limit, like in Java Edition.