This is likely due to the mix of great art galleries, shopping, night life, and high end restaurants all being in walking distance.
Most people in the middle and south of Old Town are single and generally successful. The more south you go, the more recent college graduates you will bump into; many of them ambitious and attracted to the almost Vegas-style nightlife Old Town provides.
The North and West side of Old Town generally has an older population. They are attracted to the easy living, the easy transportation, the shopping, art and overall quality of the area.