As many have said, "it depends".
The biggest you have control over is lifestyle. Your life expectancy may be bigger, but there's only so much one can do about that; other than shortening it.
As my father likes to joke, "Genetics is the biggest determinate in one's lifespan, so pick your parents well."
My wife and I could retire now, even though our youngest is in her senior year at college (we've paid for their college). It just wouldn't be the lifestyle that we want. It would probably still be a much better lifestyle than the average/median retired couple in the US, but not what we want. I want to continue flying. We both want to travel internationally, and while we won't be at the posh five star hotels we most certainly won't be staying at Motel 8 either.
My wife will retire in under two years. I've told her if she wants to retire in May when the youngest graduates, that's fine with me. Heck, if she wants to retire earlier next year I'm good with that too. I'm younger than her, and I plan on working at least 6 more years, but probably not longer than 8 years. I figure that should cover our living/lifestyle expenses with no kid expenses and no mortgage, and allow our investments to continue to grow. In conversations with my "coming-up/planning on retirement" co-workers (in our 50's and 60's), I give that 6-8 year time range which surprises some of them as I'm one of the younger of that group. I also say that I'm likely to retire when working gets in the way of my wife and I traveling.
If I do work 8 more years our investments should come close to doubling in that time. That's the plan at least.
No, I didn't throw out our numbers. They won't help you unless you want to live exactly like we do. Figure out what you need/want to live on, then budget for that.
One big thing to remember. Statistically people are living longer now. At age 65 the average person lives to their mid 80's now; a little longer for women, but only a couple of years. You will need to plan for 20 years or more of expenses. That's a long time, and it could be longer if you want to retire early and/or you have a long lifespan. So long that you will need to incorporate inflation into your numbers. That means you will need growth in your investments. No longer can you sell all of your equities at retirement and move 100% into bonds/CDs/Savings. You will need stocks, which can be done via mutual funds/ETFs, to keep your portfolio growing after you retire.