You can't use "since" there since "ages" is not a particular time. You can say "I have known her since we were both in kindergarten" but you can't say "I have known her since ages".
That is the last word. ;-)
'For' corresponds to the length of time and 'since' marks the beginning.
For answers 'how long' and 'since' answers 'when'.
Will you’re good at explaining thanks; can you help me with “then” and “than”...?
'Than' is used in comparisons. 'Then' is not.
Further to previous explanations, 'since ages ago' would be fine, in my opinion. :)