Highly doubt he can actually hack. Real hackers don't show it off to everyone for attention as it's highly illegal. If every kid who I've met online (who said that they were a hacker) actually was a hacker, my Xbox Live account would have been hacked a million times by now. Also, did you try to ban his account instead of his IP? If your server is running in online mode, he would have to buy a new account for every one you ban. EDIT by Moderator: merged posts, please use the edit button instead of double posting.
Yo, if people could hack, why would they be spending time on your server hacking, they could have just hacked the biggest server, or hacked people's minecraft accounts, also if he has HotspotShield, getting into the server wont be a problem, there's 340 accounts (Working) posted on the internet, if he knows all the passwords and emails, he can login with hotspot shield and with those 340 accounts (they are migrated, but emails come with them, so it works) and constantly griefing/spamming your server. Pretty much what I'm saying is, if he knew how to hack, your server would be a goner by now, he's just a 10 year old that just wants attention.
Its more like what eamon12 said. Also, unauthorized entry of a server is illegal. The 'hacker' is just being an annoyance, he isn't really hacking anything.