You can absolutely wear loafers with pants/sportcoat/tie. I would avoid wearing them with suits though. As for how age appropriate they are, it really depends on the style of loafer.
Since it sounds like your work situation is fairly casual, I would recommend staying away from black shoes, as black is the most formal color of shoe. My opinion (and that of many on this forum) is that black shoes are boring (many disagree, it is almost like religion). I would go with something in medium to dark brown. The AE merlot color looks good with darker grays.
As for wearing the AE casual shoes to work, it really depends on what else you are wearing. If you are just wearing pants and a button-down, then you could probably wear almost any of their more casual offerings. Some of the leathers may not work though, like the brown distressed. I would probably not wear their more formal offerings (like the park aves) with casual clothing.
As for recommending a first model, it depends on whether or not you have to wear suits to work. If so, I recommend the Fifth Ave in dark brown or the McAllister in Merlot. I would not get the Park Ave in black just yet, unless you are working in a very conservative field or plan on going on a lot of job interviews in the near future.
For a less formal office setting (sportcoats and ties) I recommend the Delrays in Chili. For a loafer, the Patriot is my favorite of theirs.
If you are only looking at sale items, the La Salle in chili is nice for $199 at Nordstrom. The Clifton in brown is nice as well (I still woulnd't wear this with suits however). The Park Ave in black is on sale at Brooks Brothers for $276, though this is still high. You can find this shoe for $199 during the Nordstrom Anniversary Sale.
Allen Edmonds stores have the Westchester loafer on sale (would get the dark brown), but I don't think it is as nice as the Patriot, so I would avoid or pay the extra and just get the Patriot.
My last bit of advice is don't buy a shoe you aren't 100% happy with just because it is on sale. Chances are, when you have acquired more shoes, you will end up never wearing that one again. This happened to me several times.