The most common and most likely answer to this crossword clue is the 6 letter word GREYER
I've seen this crossword clue in The Guardian
G
R
E
Y
E
R
Buddy explains!

The straight part
We know that "looking older" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case looking older = greyer.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GREYER mean?
GREYER adjective- Having a color.
- Having a particular color or kind of color.
- Having prominent colors; colorful.
- Influenced pervasively but subtly.
- Of skin color other than white; in particular, black.
- Of neither black nor white skin color.
- Designated for use by colored people (in either the US or South African sense).
- Having a color somewhere between white and black, as the ash of an ember.
- Dreary, gloomy.
- Having an indistinct, disputed or uncertain quality.
- Relating to older people.