Second attempt at PhD I couldn't complete the PhD at the end of third year because of unsatisfactory progress. That was three years ago. Now I am again thinking of applying for a PhD. The application requires an up to date CV. I am wondering how to mention about the previous PhD study and whether it is worthwhile at all to make such an attempt. I would be grateful for your valuable suggestions.
Yes, you must include it in your CV. Concealing it could result in all sorts of trouble later.

Your cover letter or statement of purpose should explain what went wrong last time and what will be different this time around. For example, you could discuss the job vs. studies uncertainty you had last time, contrasted with your current intention to retire and study heart and soul.

For the age concern, see How old is too old for a PhD?. In particular, I did my PhD after retirement, in my 50's, and have no regrets.