Can you give me some advice or tips for 80-years-old person traveling to Viet Nam?
I think that 80 years old person will prefer culture and historic tour which has not too much transfer. I suggest you tour around Hanoi-Trang An or Hue – Hoi An. Many travel agencies have this tour. For example, here are some tours from Discovery Indochina
Hanoi – Hanlong bay tour (4 days): http://www.discoveryindochina.com/tour/hanoi-halong-bay-extension
Hoi An – My Son tour: http://www.discoveryindochina.com/tour/hoi-an-ancient-town-my-son
Hanoi – Hue – Hoi An tour: http://www.discoveryindochina.com/tour/14days-vietnam-cultural-highlight