I think I made the age-old mistake: "Never trust a beautiful woman."
(or)
I think I made my age-old mistake: "Never trust a beautiful woman."
An "age-old mistake" is something that has gone on for years and has involved many people. " For example: Believing every word that a beautiful woman says is the age-old mistake that has ruined both beggars and princes. If you want to talk about something that you, personally, keep doing, I would use another descriptive term.
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An "age-old mistake" is something that has gone on for years and has involved many people. So, it is "the age-old mistake." For example:
Believing every word that a beautiful woman says is the age-old mistake that has ruined both beggars and princes.
If you want to talk about something that you, personally, keep doing, I would use another descriptive term. For example: