He is a old friend of mine vs He is an old friend of mine

Some examples from the web:

• He is a dear old friend of mine visiting from out of town.
• His father's an old friend of mine, and he is worried that his son might be the Dead Rose Slasher.
• Agent Jude, this is an old friend of mine.
• The head of studio security's an old friend of mine.
• - Trina is an old friend of mine.
• Just an old friend of mine.
• I showed this to an old friend of mine.
• She's an old friend of mine.
• Lucinda is a very old friend of mine.
• And he's an old friend of mine.
• You look a lot like an old friend of mine.
• He's the son of an old friend of mine.
• An old friend of mine once told me that.
• Freya, this is a very old friend of mine.
• Damian Westlake is an old friend of mine from boarding school.
• Kate's an old friend of mine from the orphanage.
• Massimo is an old friend of mine from before the war.
• -To see some old friends of mine.
• An old friend of mine married San Franciscan one.
• - No, she was an old friend of mine.

Some examples from the web:

• Agent Jude, this is an old friend of mine.
• - Trina is an old friend of mine.
• Damian Westlake is an old friend of mine from boarding school.
• Massimo is an old friend of mine from before the war.
• Sally... this is an old friend of mine.
• Ron Lewis is an old friend of mine.
• She is an old friend of mine, and someone at Raven's Den framed her for murder.
• This is an old friend of mine, show him a good time if you can.
• David, this is an old friend of mine, Charlie Venner.
• But any enemy of John Kelly's is an old friend of mine.
• This is an old friend of mine, Debra.
• Just so happens the subject of this tell-all is an old friend of mine from my modeling days, and he owes me.
• Mother, Dad, this is an old friend of mine. Mr. Brogan.
• His father's an old friend of mine, and he is worried that his son might be the Dead Rose Slasher.
• The head of studio security's an old friend of mine.
• Just an old friend of mine.
• I showed this to an old friend of mine.
• She's an old friend of mine.
• And he's an old friend of mine.
• You look a lot like an old friend of mine.