I have a lot of relatives who started showing signs of Alzheimer's and Parkinson diseases after retirement. Since they stopped being active and stopped social interactions, they started shrinking and losing their sanity. Retirement comes with a great price but no one is talking about mental and physical health.
Why should you prepare for retirement, why not continue working? Let say you have worked for too long from a certain company, and you are retiring. If you are physically and mentally fit, why con't you continue working for that company. If that company does not hire you, why not look for jobs in other company?
Retirement can damage your mental health.