I almost retired in 2007 and then again in 2010 and my current plan is 2013.
When considering retirement in 2007 (buy-out), I was awakened to the same concerns that you expressed. The buy-out offer was poor so I stayed on but I read a book by Ernie J Zelinski - The book is How to Retire Happy, Wild, and Free: Retirement Wisdom That You Won't Get from Your Financial Adviser. It is on Amazon for $9 (link below).
http://www.amazon.com/How-Retire-Happy-Wild-Free/dp/096941949X/ref=la_B001H6SY7M_1_1?ie=UTF8&qid=1347457461&sr=1-1
Read it and carefully consider and go through the thought process he talks about in the book.
The main thing is that when a person retires, they must replace three things that they got from their job:
1) A sense of community
2) A structure in daily routine
3) A sense of purpose
Using the advice in Zelinski's book, I listed all the things I enjoyed doing in the past, what I enjoyed doing now and what I wanted to do in the future.
I decided I would get into motorcycles and I wound up with 3 and enjoyed myself but "motorcycling" just did not do it for me.
Community - yes, Structure - not really, Purpose - no
I turned 55 October 2009 with 37 years and in 2010, UPS offered a buy-out again but my group was excluded and so I ran the calculations and decided that I would work an additional 18 months to recover the money I was denied in the buyout.
In early 2010 I realized I had not found that "something" that would create a sense of purpose in my life.
Again, I revisited the list of all the things I enjoyed doing in the past, what I enjoyed doing now and what I wanted to do in the future.
This time, I gave considerable thought to the Community, Structure and Purpose in making my selection.
I came up with Photography.
I investigated the business of photography and developed a 3 year development and business plan.
Set up a business and a website - Commitment
Joined 4 Photography clubs - Community
Developed a commitment to post one photograph per day - Structure
Set up a Photography processing station in my house - Structure
Enter contests - Structure
Photography jobs - Weddings, Senior pictures, Pet pictures, Portraits, etc. - Structure and purpose
Posted my images on facebook to bring a little pleasure to my fb friends each day - Structure and Purpose
Conduct photography walks and workshops - Structure and Purpose
I teach Photography at a local college in the Continuing Education program - Structure and purpose.
I am busier now than I have ever been in my life since college and I feel very comfortable with the transition into the next stage of my life.
I know this was a bit long-winded but there is no magic solution, you have to make it happen and it is a process.
Get busy planning, thinking it out, put your plan into action, measure the results and get ready for retirement.