My DS1 slept in his Amby until he was 23 months old! My niece is currently sleeping in her Amby at 13 months of age.

The standard spring that an Amby comes with can hold up to 12kg and then a second spring can be used alongside it which can hold up to 24kg. There are also heavy duty springs that can hold up to 20kg. The frame itself can hold up to 45kg so it can certainly be used for a long time .