Sentence:  It is convenient to classify a child 's onset <WSD>ages</WSD> and completion ages as `` advanced '' , `` moderate '' ( modal ) , or `` delayed '' according to whether the child 's age equivalent `` dots '' appeared to the left of , upon , or to the right of the appropriate short transverse line . 
Meaning of the word marked with <WSD> tags:  how long something has existed