It's a "new adult body", not a "newly adult body". I'm not sure having a new body resets your age. Though if nothing else, getting a long-lived body means you won't have to cast Clone as often.
Also, I looked into it and it looks like the people she's talking about died before 5e. In 3.5, it was a lot harder to undo aging. There was an epic feat for it, and I suppose Clone and Reincarnate arguably might work, but it didn't say they do, and neither could bring someone back that had already died of old age.