How much time do you believe you have left on Earth and how much would you want to have?

Having celebrated a birthday of a 90yr old friend of a friend I got to thinking how long I have lived and how many years I might possibly have left. The “birthday boy” said he never imagined he would live so long. He was married to the same gal for 61yr; longer than I have been alive. He is a great grand father many times over. If I can be lucid and mobile I thought I would like to see 100 or 103 or so but I believe I may have only 15 more good years and anything beyond that would be sheer luck or a blessing.