Can I use it as ..........?
my old friend ---------- my elderly friend

Question

Can I use it as ..........?
my old friend  ---------->   my elderly friend

Answer

No it is usually not the same.When you say my old friend you mean someone who has been your friend for a long time.IT's a problem because if you mean my elderly friend and you use the phrase"old friend" people will misunderstand you.

Answer

Not at all. 'My elderly friend' would suggest that the person at least 75 years old, and that the speaker is considerably younger.

The  phrase 'old friend' doesn't usually refer to the person's age. It simply means that this person has been your friend for a long time.