The main cast being around 15 human years old may have been the original intent, but I'd have to agree with Lurks regarding they're current portrayal as young adults with a mindset approachable to children.
And we do know at least some things about education. S1E16, Rainbow Dash was supposedly kicked out of school. AJ shows disgust for 'fancy' (or rather elementary) mathematics, FS shows hints of rather big childhood abuse (especially S2E22) making it unlikely she finished school, Pinkie as filly lived on a farm in the middle of nowhere - only Rarity and Twilight are shown attending and possibly finishing something else than elementary school, and only TS seemed to reach beginning of higher education.
It might be as you say, seeing writers are Americans, but Equestria obviously has no means of commuting, we see only one small school with one teacher, lots of pictograms instead of words suggesting widespread illiteracy (if only because only unicorns can reliably write...) and no hints anyone ever goes to big city. Example - AJ going to Manehattan like it was life-changing event, not something everyone does, and Rarity hopelessly trying to blend in in Canterlot which would be weird if she spent a few years in city on education. Heck, her awe of Twilight way back in first episode that she gets to talk to someone who lived in a place of note...
I looked at the transcript for S1E16 on the wiki, and they specifically say flight camp. Generally, when you're talking about kids attending a camp in America it means one of two things, and I'm assuming it's probably similar in Canada, either attending a private camp (usually during the summer when there is no school) or as related to an extracurricular activity through the school. The former can range from something specific (i.e. religion, acting, etc.) to something general with the focus being on outdoor activities, socializing, and fun and usually involves staying away from home. The latter usually involves staying at home, but still occurs during the summer. An example would be football or band (marching band) camp. Generally this is something that occurs near when school will be restarting and involves intense day long practices to prepare for the coming season. I could for example, be kicked out of band camp (and thus likely the marching band), but not be kicked out of school. Flight camp in this regard is probably related to more than just plain flying, something I'm willing to bet comes as naturally to pegasi as walking, and is more likely to focus on speed and/or acrobatic flying. Fluttershy says she was a weak flyer, and often parents will enroll their kids in camps or extracurricular activities to "improve" on areas they are perceived to be weak in or just because the parents feel the kid should do that. Obviously this practice has drawbacks, such as bullying from other kids in the case of kids who don't fit in or have little to no interest in the activity and who'd rather be doing something else, but mom and dad are making them do it. Rainbow Dash attending such a camp would be natural given her athletic and outgoing nature, while the timid Fluttershy, who is also a weak flyer, being forced to attend the camp would be quite plausible. The flying camp mentioned may be related to the Junior Speedsters Dash mentioned that she and Gilda were in.
Applejacks "fancy mathematics" remark in S1E3 may have been more in line with the country bumpkin stereotype being played up for laughs than an actual indicator of her intelligence, along with her over estimating her abilities. I'd argue that this is especially the case given the fact that she makes repeated remarks throughout the series regarding overseeing financial matters involving the farm and the Apple family. Likewise, the big deal about going to Manehattan probably is going along with that stereotype as well. If you were to look at a story set in a rural location prior to say the 1920's in America or even better yet prior to major industrialization you'd likely see a similar attitude, especially once you got out in the plains regions and the west. Actually, a good example would probably be any number of the old Western movies (usually taking place in the mid to late 19th century) as that is pretty much the vibe, time period wise, I got from Granny Smith's flashbacks to her childhood.
Canterlot appears to be the equivalent of Paris to the Equestrian fashion world, which would explain Rarity's awe at it and at Twilight being from there. Likewise, her difficulty fitting in there is relating to the fact that she's trying too hard to rub elbows with the equivalent of Parisian high society, in spite of her common background (actually the reason she is trying so hard). Her reaction around the window washer or her friends at the party was one of horror because she was trying to be something she wasn't for the sake of fitting in to the point where she forgot not only who she was, but also who her friends really were. That was the lesson of the whole episode.
I'm almost certain Pinkie Pie says she lived on a rock farm outside of Ponyville in the episode where she explains her cutie mark. That would indicate to me that it relatively near, but outside the city limits. Sweet Apple Acres appears to be just outside of Ponyville proper, so it may be that the rock farm is even further away (say maybe a day or twos travel time by foot). She is about the only one whose childhood might preclude what we'd consider a normal education, though that also makes her a very good candidate for some form of commuting. We do see quite a few forms of travel in the show, so I would not rule out commuting. Babs arrives at the family reunion on what appears to be a taxi (whether that is all the way from home or just from the train station in town to the farm is unknown). We see a tour bus in the Mysterious Mare Do Well along with mechanized floats in Babs Seed. We see airships in several episodes and of course the train, hot air balloon, and carriages/coaches featured in others. When Sweetie Belle stays with Rarity she refers to her fathers wagon in much the way one would refer to a personal automobile. Ponies are certainly not lacking when it comes to non-pedestrian means of travel.
The non-unicorn ponies are shown writing with their mouths, though that may lead to decreased written word and heavy use of mechanical print and pictograms compared to humans. Signs in the shape of what the store specializes in are certainly not uncommon in the real world, though they are less common than they used to be. Pictograms are also extremely common as well. For example, just about the only traffic signs in the U.S. with written words on them are those that identify a particular location or road by name, speed limits, and signs commanding the driver to stop and/or yield to other traffic at a particular location. One does not need to be able to even speak or read English, the only language in my experience that road signage is printed in, to be able to legally be licensed and operate an automobile.
Finally, I honestly doubt the show writers have given much thought to education. The fact that Ponyville seems to have only a small one room school house with a lone teacher probably has more to do with romanticizing the notion than any thing else. Such a setting allows for more personal interactions between not only the students and the teacher, but between each other.
