Board Thread:Episode Discussions/@comment-1181222-20180411104401/@comment-4904146-20180411195330

In the manga, Himawari is at the age of 7 during the Chunin Exam Arc. That's how many candles were on her cake during the birthday scene. Making her 5 years younger than Boruto, who is at the age of 12.

Some of us fans know that she is at the age of 10 during the Chunin Exam Arc in the anime because she is two years younger than Boruto.