What's the origin of the colloquial "peachy", "simply peachy", and "just peachy"?

Question

I found a few connotations of how the slang "peachy" is used:

1. Vocabulary.com: #1: very good [non sarcastic]:

   If you're unhappy, it's usually best to be honest about it, rather than pretending everything's peachy.

2. Merriam-Webster Thesaurus: "of the very best kind" as in lovely:

   a look back at those innocent days when the offerings at the local soda fountain might have been described as "simply peachy"

3. Wiktionary #2: (colloquial) Very good, excellent, typically used sarcastically to indicate a state of misery, resentment or great frustration:

   Oh, life is just peachy now that winter has come, it’s snowing all the time, and I’m freezing my backside off

What's the origin of this American slang, and how did it become more common today to use peachy in a sarcastic way?

Answer 1

Peachy meaning very good, excellent, is derived from the sense of peach used metaphorically to refer to a pretty young woman. Such usage dates back to the 16th century.

1- a pretty young woman (see Williams for fig. uses of peach in 16C–17C).

• 1754 [UK] E. Turner letter 16 Aug. in Dickins & Stanton 18C Correspondence (1910) 238: I had almost forgot that orange Peach, your Niece.

Early usage extension in ironic sense appear to start from the 70s.

ironic use of sense 1

• 1979 [US] G. Swarthout Skeletons 48: ‘How are you, darling?’ ‘Peachy keen. I got a speeding ticket.’.

(GDoS)