The thinking behind it is fairly sound... they are free from political interference once they are appointed. We have the same justification. But for some reason (partly religious, imo) they tend to rule with whomever appointed them. Our courts are much less partisan. And, our SC is appointed to age 75, I believe...
It isn't sound at all. No one can perform at the same level in their eighties and nineties as they can in their sixties and seventies.
The fact they are picked as political entities according to their political and social views makes it even worse.
I used to be an admirer of the US system but they have made such a mess of it, I no longer have that opinion.