Jonathan Richman’s career has proved so long-lasting -- more than 35 years now -- because he is seen as the eternally endearing manchild. At age 57, he still has the looks of a boy, an adorable waif maybe -- lean with dark hair and staring eyes, a knowing smile and an oddly punctuated, affectless speaking style that suggests a youngster proudly making declarations (“Yes, I can walk!”) to amused adults. Many of his fans see him as a lovable, high-energy Comedy Rock act with an attention-deficit disorder only relieved by dancing. Richman, the perpetually endearing manchild, performs his minimalist, almost-outsiderish Folk Rock at The Southgate House.