I planned to retire at 65. That was when everyone retired, wasn't it? ;-) It's probably just as well I didn't have a hard and fast plan back then; marriage followed by a child at 31, spouse who was a financial train wreck, divorce, remarriage 7 year later, move to a LCOL area... none of that was in the spreadsheets!
Two memories did make me question my assumptions: first, when I was 27, coworkers were talking about a guy they knew whose company told him he was being promoted. He told them he didn't want to be promoted. They told him he had no choice. He ER'd because he had enough investments to do so. My Dad was demoted from his job running a branch of a major steel company when I was 32. He and Mom sold the house in the Midwest, moved to Myrtle Beach and eventually bought a place there for cash.
It drove home the point that it was good to build up a cushion so you have options in your 50s/early 60s. I ended up retiring at 61- job turned sour, didn't want to look for another one, end of story. Life is good.