Indian summer

noun2

1. •
   (offensive) A stretch of sunny and warm, often hazy, days during late autumn.

   • And while the bards, before my fancy bring / The Indian summer, and Italian spring, / Rapt let me mark the different climates found, / In Temple's gardens, and his lawns around. — 1786
2. •
   (figurative) The late autumn of life; a late flowering of activity before old age.