How far back do you think your LO can retain something in his/her memory? How old are they?

M is 9.5 months and I would say she has a good 2-4 weeks memory at least of significant items.
I can say this because our really good friend D is her 3rd favorite person in the world. Next to mom & dad of course. But we only see him & his wife once a week sometimes every other week. But every time she sees him she is SUPER excited, smiley and giddy! Been that way since she was old enough to "play"