Yes, Biden is old. Yes, the job of the president ages you fast. That is if you take the job seriously and work at it. If you spend the time fooling your base and playing golf? You won't.
Having said that, everyone dies. Even young people. Even young presidents. The youngest president who died of natural causes was James K. Polk, who died of cholera at the age of 53.
So, will Biden finish his term in office? If I knew that, I could bet on the Powerball and retire a very rich man.
Let me know if you are still confused.