strong and healthy (Oxford)
able to survive being used a lot and not likely to break (Oxford)
(of a person or animal) strong and healthy, or (of an object or system) strong and unlikely to break or fail (Cambridge)
She was almost 90, but still very robust. (Oxford)
We have a robust pair of walking boots. (Cambridge)
robust in old age
robust pair of walking boots
Vigorous
Sturdy
Weak
Enervate
Robustness
Robustly