It's not bad. I think it'll definitely need dressing up with something though - especially to make it into an outfit for a 26 year old.
The top worn with the dress in black (the lace top) is a cute look for going out I think - with some black heels and some gold accessories.
Otherwise as day wear maybe with a crisp white shirt under it and some chunky bangles. Tights or leggins would also go well with the dress, but if you have the legs, and the weather's good - I don't see why you can't wear it with nothing on your legs.
I can see it working with gladiator sandals too and a light-weight cardigan.
There are lots of things you can do with it being such a basic design and I wouldn't wear it just on it's own.
First day of what? School? A job? If it's the latter, it's definitely not appropriate unless you work at an ice skating rink. Personally, I like American Apparel but some of their clothes make no sense to me. It's not that it's childish looking, but the fabric they used looks cheap and kind of tacky. Then again, I've seen people pull things off that I'd assumed would look hideous so if you think it looks nice, go for it.