What is Naruto's age? I'm sort of new to Naruto. I just finished most of part one and about to start Shippuden. I was wondering how old was he at the start of Shippuden? I'd really like to know as I have researched it a bit and can't figure it out. Maybe it slipped by me.

There's been all sort of answers online, but no definitive evidence. Evidence would be nice.
From the wiki under Personal

Part I: 12 - 13
Part II (Shippuden): 15 - 16

It is also worth noting that when Minato asked him his age after stoping naruto from releasing the Kyuubi's seal, Naruto told him that he was 16.
On the wiki, it also says that he graduated from the Academy at age 12, some time passed and we know he spent ~2.5 years away training with Jiraiya so accounting for any time that may have passed, it eventually adds up.