I greatly doubt the translation for that “live longer than Nan mountain” is correct.
Firstly, the sentence isn’t about long or short
Secondly, Originally the adjective used was not comparative either.
The wish traditionally is about a folklore.
The Southern mountain is known to have immeasurable number of Phyllostachys. So many that people can’t count. The wish in its word to word translation is to wish for the Elderly to live as many years as the number of Phyllostachys on the Southern Mountain.
Sometimes, kids can make modifications of this traditional wish by replacing the meaning from “wishing grandparents to live as many year as Phyllostachys in southern Mountain” into “wishing their relatives to live even more years than the number of Phyllostachys“.
Whatever the case, I don’t know the raw so I won’t bother further about the second point but the translation of the wish is very sloppy, lacking in poetry and skillful use of words.