If I see a resume from a kid fresh out of college that didn't even last a year in their previous/current job, unless I know the company to be exceptionally crappy I'm gonna assume that kid's a quitter.
Just to name a few: the job description didn't match the actual job, overbearing managers, overbearing coworkers, uninteresting work, a better offer elsewhere, changing interests, or - just like OP - the employee feels like he would grow his talents better elsewhere. I have been in the same situation and employers have understood and respected my decision.
This career's not easy. This career's not always fun. There's strong personalities all over. Sometimes the going gets tough, how do I know this person's going to get going or just get gone?
Spending less than a year in the first job would be a red-flag for me, and it would take the candidate offering some very persuasive reasons for having left for me to give the serious consideration.
But "I wanted to do something cooler" isn't going to cut it, because how do I know they won't find something cooler six more months down the road.
If the environment is hateful and you're going home in tears every night and hitting the grolsch a little too often then yeah you gotta do what you gotta do, but that's how things are.
We generally look more closely at employees who quit or are let go quickly, but we don't treat the involved companies with the same level of scrutiny.
It's hard to actually do that, because employers don't provide a company resume at the interview that details the list of employees that they've worked with, and the accomplishments related to those employees that show off the company's skill and responsibility. I also don't recall ever seeing a company give references to a prospective employee; at best, a candidate might get some cheer leading from a colleague who's a current employee.
If you have someone who makes it to 35 and doesn't have a stint more than a couple years, then you have a quitter. But it's really common for new grads today to have 3-4 jobs in their first couple years out of college, then a longer stint of 4-5 years as they find their footing.
The most important thing at any job in software is to always feel that you are improving as well as contributing to the organization's goals. The latter is often true, but the former is your part of the bargain. We are fortunate to live in a world where employment is high and you can and will find a job where those two needs are met. Take advantage of that because no matter how "great" of a culture the organization that employs you has, if they don't offer you constant improvement and opportunity, you are at an economic loss that can affect your career much more than it will affect their future.