A lot of the residences around 4th ward are very walkable. There is a Harris Teeter grocery in 5th and Poplar and entertainment/eating options are not far away at all.
I own a rental unit in a building across from 5th and Poplar (Park Plaza), it is currently vacant (don't know if you are renting, but DM me if interested).
Aside from my place, there is a building on the other side of 4th ward park called Jefferson Square that is comparable to 5th and Poplar. There is a very nice town home complex next to the park called Park Place and further up 7th St is 400 N. Church (Rock Bottom brewery is in this building).
I don't know of any buildings catering specifically to an age range, but I know my building has a very good mix of ages as do the others from what I understand. There a lot of other buildings other than the one's I mentioned also... if you are purchasing, you will have a lot to choose from.
Good luck, I hope that helps