Everybody is saying that he is 10 in the anime (he might be in the current Sarada Gaiden arc), but in actuality he was only 8 (at least in the Sumire arc).
In the beginning of that arc, Iwabe stated that the war was 10 years ago. We certainly know that Boruto wasn't born during the year of war. Naruto and Hinata got married at age 19 (which was 2 years after the war). That is the earliest point at which Boruto could have been born. Since it was 2 years after the war that was stated to be 10 years ago, then Boruto would at most be 8 (by the beginning of the Boruto anime).