Is it a disadvantage to learn on a guitar that size? I have read in some places that it is?
There's sort of a tonal "disadvantage". if you can call it that. Smaller bodies trend toward being fairly bright. If that's what you want, there isn't a problem. When you're playing solo though, you do have to, (or should) work some bass notes into your playing. Big bodies have better bass, which can balance out even a fairly bright guitar.

With a smaller body, you might have adequate bass, you might not. That's sort of a balance of personal taste and fact, so it's pretty much up to the player's judgment.

Assuming we're talking about small, but still standard scale length.. (24.75" to about 25.5").

Smaller guitars ride a bit lower in the lap, and also place the neck / body joint closer to your side. I find that they can jamb you up a bit when you start playing higher up the neck. (The "classic" position for playing a "classical" guitar, is with the lower bout of the guitar in BETWEEN the legs, which moves your fretting arm away from your body, alleviating that issue). But, truth is most rockers or folkies wouldn't be caught dead playing with that posture, and that's when the bigger body comes in handy, moving your fretting arm away from your body..

So here it depends whether you plan to do most of your playing seated or standing. It also it depends somewhat on the stature of the player. That having been said, Emmy Lou Harris rocks a Gibson J-200 super jumbo on stage, seemingly without much trouble at all.

Larger body guitars generally require heavier strings to give of their best, particularly in the bass. All things being equal with respect to neck width, radius, and action height, heavier strings will require a bit more fretting effort.

The enhanced bass of dreadnought and jumbo guitars is what makes them so popular, especially for laying solo. In the context of a band, a brighter guitar might be able to "cut through the mix" better. With that said, I tend to EQ my guitars differently, depending on whether I'm playing by myself, (bass boosted & treble cut), or playing along with the stereo. (Here we punch up the mids & highs, and drop the bass), so your guitar doesn't interfere with the bass player doing his thing.

You should only consider anything you hear as suspect, as we're all different. As far as I'm concerned picking out an instrument because, "so & so uses one like it", is a bit foolhardy. Remember that so & so isn't you either, and you should look, listen, and play guitars, until you determine what is going to work for you.
There seems to be a bit of a fad currently for small-bodied "O", "OM", and "Parlor" sized instruments. They have always been popular with fingerstyle players due to the somewhat more-balanced sound.

Quite a lot of companies are now featuring such instruments in their lineup. I bought a Taylor GS mini a few years ago primarily for the ergonomics. An old guy with wonky shoulders.... I was finding dreadnaught-sized guitars painful to play. The Mini is pretty close to an "O"-sized instrument and has a short scale to boot. I find it very pleasant to play, and it seems to work well for both fingerstyle and flatpicking.

The only disadvantage to playing such for a beginner might be the transition to a full-sized instrument if you want to do that at some point....But I certainly didn't have any such problems going the other way...
I play on a small First Act guitar, I really would like a Martin LX1E like Ed Sheeran's but just do not have the money.
The only disadvantage is what Bikewer said, I'm not used to the full sized instruments. But it isn't that hindering I feel.
OK, that LX-1 is uncomfortably close to a baritone uke for my taste.

Actually Sheeran was on the Victoria's Secret Fashion Show this year, playing a Strat. I liked that better....

DISCLAIMER: The opinion expressed is strictly that of my own. Your opinions, feelings, personal taste, and results, may differ.
Last edited by Captaincranky at Dec 21, 2014,
I tried out an LX-1 last summer at the Martin factory. It's a nice sounding instrument but, for a guy my size (6'1", 200 lbs.) it's not a primary instrument. If I were doing a lot of traveling with my guitar, it's something I'd consider.