Working a full time job + Running unattached

You should be able to have plenty of time to train optimally if you are working 40 hours per week, as long as you don't have a lot of other commitments; you just need to find 1-2 hours to train each week day. If you are working more that 40 hours and/or have a lot of other commitments (ie family or college courses on top of work) its still possible although you probably won't be at top form. I'm not sure what it is like to get entered into an all-comers meet sponsored by a college, but generally there are lots of weekend 5Ks around. I would recommend finding a community running club if you live in an urban area or a running group on meetup.com.

As the above poster mentioned the more commitments you have the harder it becomes to fit in a workout. Currently, I work a full time and part time job, working on a teaching credential, and have a family. The only time I have to workout is 4:30 in the morning. The biggest disadvantage I face is not being able to get a solid 8 hours of sleep to fully recover from workouts, most times I have to adjust my workouts depending on how my energy levels and legs feel.

But with enough determination you can do it. You are just going to want it bad enough. That's the only thing that gets me up in the morning.

You can do it. Back in the day a lot of runners were world class and worked- no true pro's back then.

But, like they said, you have to limit commitments so you have time to do, preferably, doubles.

Yuki Kawauchi has run a 2:09 marathon while working full-time.