I'd expect most of the audience will be in their 20s and 30s, with more 20s than 30s; most mods fall into that range too. That age range has been typical of the blog audience, although there are plenty of senior readers too. I think the younger crowd is the age group that's most interested in reading blogs. It's also an age range where people begin getting interested in personal development.
I'm 35, which is actually pretty young to working in this field. Most of the popular writers and speakers in the field are in their 50s and beyond.