There's nothing inherently wrong with "an older neighborhood." What really matters is the quality of the neighborhood, and whether it's stable, improving, or declining. I know the area somewhat. With all the road construction (Woodrow Wilson Bridge, etc.), the roads that feed into the Beltway can get congested at times. But the neighborhood has a lot going for it. (And if it's the property on the market, priced at $xxx,888, it's a very good value. That agent prices properties very, very attractively.) I'd trust your Realtor on this one.
Hope that helps.