Synonyms for Way back when:

• adj.

  •past (adjective)
  • bygone,
  • quondam,
  • over,
  • ex,
  • late,
  • prior,
  • olden days,
  • previous,
  • old,
  • Latterday,
  • latter-day,
  • sometime,
  • way back,
  • time was,
  • gone by,
  • foregoing,
  • ages ago,
  • once,
  • latter,
  • behind one,
  • erstwhile,
  • gone-by,
  • bypast,
  • ex-,
  • good old days,
  • retired,
  • earlier,
  • down memory lane,
  • back when,
  • long ago,
  • long-ago,
  • preceding,
  • early,
  • way back when,
  • one time,
  • one-time,
  • ancient,
  • recent.

• n.

  •ancient history (noun)
  • antiquity,
  • time immemorial.

• Other synonyms:

  •
  • formerly.

Antonyms for Way back when:

• adj.

  • past
    present, current, future.