I would be sceptical of hiring somebody that has been code monkeying for 20 years, as in still making the same mistakes they were making 20 years ago. It's a smell of somebody that doesn't warn to learn new things, and has no commitment to quality in any sense of the word.

On the other hand, somebody that has deeply learned their craft and is still actively learning makes a very attractive employee. Age and number of years on the job by themselves say nothing about ability.