92. Positive or comparative? 

• Incorrect: He is becoming strong.

 • Correct: He is becoming stronger. 

• Incorrect: She is getting young. 

• Correct: She is getting younger. 

The sentence 'He is becoming strong' is of course correct English, but the English language has a special fondness for the comparative adjective, instead of a positive adjective, when growth or change is implied in a sentence. 

For example when we are talking of a boy's progress in class, we often say 'He is working better now' thinking of a time past when he worked less