辈 is a phono-semantic character. In the seal script, 辈 
= 
(非) + 
(車). 車 acts as semantic component and 非 phonetic.
車 represents ancient chariots. The phonetic component 非 indicates that the chariots are arranged in parallel because 非 is like a pair of wide-spread wings. The character 辈 depicts a row of chariots.
The original meaning of 辈 was extended to:
1. people of a certain kind, e.g. 我辈 people like me; 无能之辈 incompetent people
2. generation, e.g. 老一辈 older generation; 他们同辈 They are of the same generation; 老前辈 one’s elder; 晚辈 younger generation; 祖辈 ancestors
3. lifetime → 辈子, e.g. 后/前半辈子 second/first half of one’s life