I think it's pretty essential for the characters that they are all aged, especially Daenerys, but Bran and Rickon as well: the older Rickon is actually treated as a squire, running around getting weapons for people etc, which is a nice touch and true to the setting, whilst he's still young enough to be confused and unsettled by what's going on.

The only problem with the aging is that we loose at least one scene between two characters who are only two years apart in the books but more like six or seven in the TV series; the bigger age gap makes the idea of them having a confrontation a bit silly.