Janet wrote:

There are two separate issues. The first about picking weakening the
plant applies only to new plants.

The other , is about the level of oxalic acid in rhubarb; which
increases as the growing season progresses, and is the reason it's
recommended not to pick/eat it after midsummer. Especially for the
elderly, small children, and anyone with kidney stones or gout.

Or rheumatism or osteoarthritis.

--
Rusty