Here is my list of reasons why there is no need for that:

1. Jaskier in the books is described as looking ‘almost thirty’. Joey looks almost thirty. Perfect.

2. Dragon hunt (01x06) happened in 1262, Battle of Sodden in 1263 (02x01). I don’t think there will be more than 2-3 years between the last time we saw Jaskier when we’ll see him again.

3. They didn’t age him in season 1. If they wanted him to look older they would cast an older actor. Making him wear weird makeup for the next x years just doesn’t make sense.

4. Joey with a beard looks like a different person. They can’t change his image too much, because he still has to look like Jaskier. Maybe a stubble or a little bit different hairstyle, but nothing drastic.

The only reason why they would want to age him is because they didn’t do it in the first season and people were confused why he looks the same all the time. But they can fix it by some character commenting that he looks too young for his age or something. I don’t know, I don’t feel like there is a need to change anything in his look.