Somewhat given that in the novels it mentions that when Shisui meets 5 yr old Itachi for the first time... he is a genin, considerably taller, and did not graduate from the Academy early making him at the very least 12, perhaps older if he had been a genin for longer. Probably longer, given he had been going on missions for some time, had a former best friend, and killed said best friend out of jealousy (his best friend was from a fodder clan but more skilled) which led to him getting MS.
Perhaps Studio Pierrot changed it in order to make things less awkward? Having a 12 yr old ask a 5 yr old he barely knows to be his best friend just because he's talented may seem a bit odd/pathetic on the former's behalf. In hindsight, that is a little non-sensical because Shisui could have asked a talented kid from outside the Uchiha to be his best friend that would be closer to his age instead.
Or they'll just use the same canon ages for them but use the excuse that Shisui looks young for his age. lol
Or even gloss over the crime Shisui committed to get his MS, not mention it, and just show him with MS so that his age is not called into question (as he would need to be considerably older to do something like that given he had it before meeting Itachi).
ot: Not only that, but they added a voice actor for Shisui's child version which has never been voiced before (his voice actor is staying the same for his adult version).
And Hideo Ishikawa is still voicing Itachi's teen/adult version but for his child version they added a new voice actor (since when Hideo Ishikawa voiced Itachi in former eps, the voice was too deep for a small 5 yr old child- deeper than 14 yr old Kakashi and Gai lol). The voice actor for Itachi from ages 4-8 is going to be Yuka Terasaki from now on.
