Did she have a precursor? She did, indeed she did. In point of fact, there might have been no Lolita at all had I not loved, one summer, a certain initial girl-child. In a princedom by the sea. Oh when? About as many years before Lolita was born as my age was that summer.
(Lolita, Vladimir Nabokov)
I can see the as~as expression, two adverbial: ‘before Lolita was born’ and ‘that summer’ in the highlighted part. But with this I can’t understand the phrase at all. Would you show me the meaning with parsing?