The last time I saw you was ages/has been ages ago
Interestingly, of your choices, I'd have said, The last time I saw you was ages ago.
However, in AmE, we usually simply say, It's been ages! which means, It has been ages, or, I haven't seen you in ages.
But not the last time I saw you has been ages ago. Saw is the past tense. It was done. Has been is the present perfect progressive tense, and describes an action that began in the past, continues in the present, and may continue. The two don't go together in a meaningful sense without some other construction.
It has been ages since I have seen you. The tenses match here.