The most common and most likely answer to this crossword clue is the 6 letter word SENILE
I've seen this crossword clue in Financial Times
S
E
N
I
L
E
More clues leading to the result SENILE
- Like some old folk from home counties on foreign river
- Doddery earl with signs of ageing all over
- Old Eastern Railways diverted northwards
- 8 Consider eating nothing, if confused
- Old face finally wrinkles up
- Observe nothing in being old and infirm
- English band’s backing ‘Gaga’
- Old Kentish river?
- Home Counties river showing sign of decline?
- Some of the lines go up doddering
Buddy explains!

The straight part
We know that "Old" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old = senile.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 SENILE mean?
SENILE noun- A person who is senile.
- Of, or relating to old age.
- Exhibiting the deterioration in mind and body often accompanying old age; doddering.