'She's fifty years old if she is a day old'

I am probably very thick but I can`t really see the point of the saying "If I`ve heard it once I`ve heard it a hundred times." I do realise the meaning behind it, but it still doesn`t make much sense to me. Anyone feel the same?

The expression you refer to is similar to this one: 'She's fifty years old if she is
a day old.' Anyone who says this does not mean that being fifty follows
from being a day old. The speaker is using the sentence to emphasize the
claim that she is fifty. Likewise, one who says 'If I've heard it once ...' is
emphasizing the claim that what is being heard is tiresome.

Interesting example you use there Fred, cos that one makes even less sense to me than the 'If I've heard it once ...'. I know it's an old one and I've heard it often myself, but never really thought about it.

I agree and understand that it's emphasizing the fact. However, I can't make much sense out of the actual words 'She's fifty years old if she is a day old'. ie. How can she be 50 if she's a day old? I really don't get it.

What is meant by the speaker is that it is as obvious that she's 50 years old as it is that she's a day old. Hope that flies below the follicles.