The most common and most likely answer to this crossword clue is the 6 letter word AGEIST
I've seen this crossword clue in Independent
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More clues leading to the result AGEIST
- One who stands against the old decaying gates enclosing unit
- Blocking peerage is terribly prejudiced against seniority
- A European, in essence, is a discriminating sort
- One opposed to people getting on?
- Bigot adrift touring Spain
- Prejudicial to those getting on revolving stage without electric current
- A spirit favouring youth
- A good site for redevelopment — one with narrow horizon?
- Spirit of group getting behind a discriminator of old
- One won’t stand for old people!
Buddy explains!

The straight part
We know that "One opposed to people getting on" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one opposed to people getting on = ageist.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 AGEIST mean?
AGEIST noun- A person who behaves in an ageist manner.
- Unfairly discriminatory against someone based on their age.