Most people are still reasonably fit and active when they retire. Moreover, now that they no longer have the impediment of work, they have the time to do things; time to shop, time for leisure activities, time for sports, travel, socialising, and entertaining grandchildren. All of these things cost, but chances are that you will do less of them as you move further into retirement.
In fact, I do not think it especially useful to think of retirement as one stage of life. Instead, it is best to think of retirement as three stages, each with its own characteristics and (crucially) expenditure levels.
Retirement is for a long time: a 65-year-old woman will have a life expectancy of nearly 90 – that is 25 years in retirement. Over that time, you will change. Think of another 25-year period of your life, say from age 30 through to age 55: you were quite different as a 55-year-old compared to your 30-year-old self. You lived differently, you did different things, your work was different, and your expenditure was different.
So it is in retirement: 25 years on from the start of retirement, the things you do and the way you live will change – and with that change will come changes to your expenditure patterns.
Rather than just one stage, it is better to see retirement as three stages: