Age alone is not a reason. A filling that is sealed, sound, and not causing problems is usually best left alone — every replacement removes a little more tooth.
The seal has failed and bacteria are getting underneath.
A fracture in the filling or tooth
Structural, not cosmetic.
An open margin
A gap you can catch a probe in.
Recurrent sensitivity
Especially if it is worsening.
Cosmetic reasons, front teeth
A legitimate reason when the patient wants it — stated as cosmetic, not as necessity.
On replacing silver fillings
A sound amalgam filling that is sealed and not fractured does not need replacing on the grounds of being amalgam. Removing it means removing more tooth structure and, in a large filling, may commit the tooth to a crown.
If you would prefer a tooth-coloured restoration for appearance, that is a valid choice — it should simply be framed as a preference rather than a clinical necessity.
What we can explain here — and what needs an exam
A page can inform you. It cannot examine you.
We can explain online
What a failing margin is
Why every replacement removes tooth structure
The difference between necessary and elective replacement
Determined after an exam
Whether your filling is failing
Whether a replacement filling or a crown is appropriate
Whether decay has reached the nerve
What to do next
Ask which category the recommendation falls into: failing, or elective. Both are reasonable answers; conflating them is not.