You can't teach an old dog new tricks.

You can't teach an old dog new tricks.（老いた犬に芸は仕込めない）とは歳をとると頭が固くなって使いづらくなるくらいの意味。0;01 they say you can't teach an old dog new tricks but this pup from China can perform 40 different stunts. 歳をとった犬には芸は仕込めないというけれど中国のこの犬は40の芸ができる。注；pup (= young dog) だから芸ができる、したがって、老いた犬に芸は仕込めないとの矛盾は無い。

https://www.youtube.com/watch?v=1AdzRpV8ym0  42:56 You can't teach an old dog new tricks.
https://www.youtube.com/watch?v=qDK8hMvNz6A  1;29 you can teach an old dog new trick. 歳をとっていてもまだ使える。
https://www.youtube.com/watch?v=cJdseqWvEvY  0:03 you might not be able to teach old dogs new tricks but you can give them good homes. ワンちゃんに芸を仕込めなくても寝床を与えることはできる。

0;57 did they teach his old bot some new tricks?

Boston Dynamics teases updated robot dog, SpotMini

参考リンク
https://www.youtube.com/watch?v=0hyBK1ZphGE  0:05 you're never too old to try something new.

練習問題解答
a-4742 you can teach an old dog new tricks