a long time ago; a generation ago; in the old days
Refers to a time roughly one generation or a decade or so in the past, not ancient history. Often used when contrasting past customs or situations with the present.
A generation ago, few people had mobile phones.
This town has changed a lot from what it was a generation ago.
Standard kanji spelling.
Mixed kanji-kana spelling; less common but still encountered.
Compound of 一 (one) + 昔 (old times) + 前 (before), literally 'one old-time ago'. The exact span is vague but typically understood as about 10–30 years.