You should begin planning several years before the date you have set for retirement so that you will know what is required to continue certain benefits into retirement. There are many factors related to retirement planning, and it is literally never too early to begin.
Becoming eligible to retire is great on paper. The main question that needs to be considered is will you be able to retire financially, enjoying the retirement you worked so hard in federal service to have. Many do not take into consideration certain aspects that are out of their control like rising taxes, inflation, healthcare costs among other things.