I would like to second this suggestion.

I do wish I had thought to put even a little money away for retirement when I was in my 20s. It just never occurred to me. You can park it in an IRA and forget about it, and it will do the growing on its own.

If you are like me, the places I worked in my 20s didn't even have retirement plans, and I'm not sure IRAs existed back then. I wouldn't have even known how to put money away for retirement. But it is really easy today with all the mutual funds to choose from and IRAs.

If you have as little knowledge as I had about those things, you would not know what mutual fund to choose. So here are two ideas:
1) choose a mutual fund indexed to the stock market
2) choose a mutual fund that has a targeted retirement date--it will have a certain mix of investments right for your age that changes as you get older. So if you are 25, choose one for people who will retire in 40 years.

Index funds have very inexpensive expenses (fees you pay to have the fund managed) since they are not actively managed. So you can save a little bit with this type of fund.

The staff at big mutual fund houses like Fidelity, Vangard, etc. will be very happy to help you choose a fund and get the IRA started.