The world has many old ships- HMS Victory, Warrior, Pride of Bilbao, that are all old yet keep on going. America has many WW2 ships (as do many other countries), which many of these are older than QM1.
They still float. The point is not when it reaches the age where it can no longer be maintained- it is the age where people say it isn't WORTH being maintained...
Look at a 10 year old car "failed its MOT- let's scrap it"... Yet there are people with cars decades old, who DO spend the money...