The most common and most likely answer to this crossword clue is the 5 letter word ICENI
I've seen this crossword clue in The Times
I
C
E
N
I
More clues leading to the result ICENI
- Old people off home to reflect
- Old people’s home hooked on methamphetamine
- Old people’s home, one civil engineer visits
- Old folk freeze at home in retirement
- French here penning in rebellious Brits
- Old warriors showing reserve, approaching province
- Old tribe pleasant, beginning to end, on island
- One with terribly nice old folk
- Lack of warmth in retiring old British people
- Old people I notice close by, within hearing
Buddy explains!

The straight part
We know that "Old people" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old people = iceni.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.