"However" vs. "but"

In the question sentence:

He is seventy-five, he still__ (but, however) pays regular visits to his old mother.

Which word can be put in the blank? The answer books says "however" but it sounds quite odd to me. Can however be used in this discourse context, and why?

Solution 1:

"However" can be used provided it's set off with commas and the comma splice is fixed somehow.

He is seventy-five; he still, however, pays regular visits to his old mother.

Though he is seventy-five, he still, however, pays regular visits to his old mother.

You can use "but" so long as you put it earlier in the sentence.

He is seventy-five, but he still pays regular visits to his old mother.