Ahhh...it is perhaps brazen for Grasshopper to add to the wisdom of Master Paul, but...

Two thoughts to toss in the mix for you.
1.) Is the employer's profit share distribution based on your 401k participation?
My last employer's was and those that didn't participate in the plan missed out on some free money each year.

2.) How disciplined are you to save money from your paychecks to fund an IRA?
If I dig into my unreliable memory banks from when I was around your age, I recall that I only was successful at doing this once in the 5 years before 401k's were offered.
When I started up in a 401k, it imposed the discipline I was missing since the money never touched my grubby hands. It seemed like menial amounts at the beginning, but once the balance grew to a few grand, that was soooooo motivating and I quickly escalated to maxing out each year by bumping my contributions to offset each raise.

Guessing from your screen name, you're in a fun part of town, so you're probably struggling with wanting to keep some mad-money free to enjoy it now as well.
At any rate, congrats on adopting some Foolish thinking so young. In hindsight I wish I would've, but then again, I have some damn good memories from the things I did while spending it so foolishly.