Can a semi-serious relationship exist? Of course. But it probably won't last. (Believe it or not, its possible to have serious relationships that don't last forever!)
Is it likely? No.
Is there a chance that a not-so-serious relationship can grow into something more? Yes, though it's more unlikely.
Yeah, a few issues as to why it probably won't last assuming you find someone who's even interested:
1. You don't know who you are yet. This means you likely don't know what you want, and its unlikely what you end up getting will fit that. Some people don't figure this out (or any of these points) until well into their twenties. (some never do)
2. Even if you know who you are... You'll change, most likely to a person who doesn't like the person you're with or isn't liked by them. And knowing who you are doesn't necessarily mean you understand what you want.
3. Above two, but for the other person.
4. Eventually, you'll both grow into people who realize what they thought was important wasn't, and break up, assuming you now know the truth. (This will not be true)
5. Eventually, you'll discover what IS important - if you make it to this stage while still together, there's a good chance you'll go all the way! Unless one of you decides that what's important is something other than the relationship, and it becomes an either/or situation (world travel, professional career, there's many causes of this)
6. Most high quality relationships are based on a concept of self-sufficiency. Knowledge that the other person CAN successfully/happily live without you, but doesn't want to. If that's not there, a relationship can quickly end up feeling like a burden, which isn't good for anyone! And since you've likely only ever been reliant on others and not on yourself, you're very unlikely to have this!
Now, here's the important bit:
This doesn't mean you shouldn't try.
Experiment while you can. Work on addressing those points - find out more about who you are and what you want (and in some cases, its more about deciding who you are than discovering it), because it's usually pretty vital to a high quality relationship. You don't really need to deal with all of them for a relationship to be serious or even successful, but they help.
If you're interested, go on a few dates with her! Discover some stuff together, ask her out. Don't expect it to last forever, even if you want it to, but god knows breaking up in middle school doesn't mean you won't ever get back together (unless you really like burning bridges).
And finally-
This could all be bullshit. I didn't date until Uni.