the.com/heyday

that golden stretch when you peaked and didn't even notice until later.

means The period of someone's or something's greatest success, vigor, or popularity.

from From the old exclamation 'heyday!' — a cry of joy or surprise, like 'hey!' with a flourish, recorded from around the 16th century. The 'day' part is a bit of a trick: it likely had nothing to do with daytime originally, but the spelling drifted toward 'day,' and over time the word slid from a shout of high spirits to the idea of one's high-spirited prime.

origin
From an old cry of joy, not the word day.
the high
Originally meant a state of exhilaration, not a time period.
shifted meaning
Day got attached by mistaken folk logic.
timing
You only recognize yours in the rearview mirror.
for instance

british empire — controlled 25% of world's land and 400 million people at its peak around 1920

hollywood golden age — 1930s-1950s when studios like mgm dominated global cinema and created major stars

beatles 1964-1970 — band sold 600 million records during their decade-long peak dominance of pop music

the.com · every word