I think the first sentence means the 'change' was an event -so to speak - and has finished (even if the consequences of the change persist) - that is, 'change' is not present and continuing; the second reflects that the wearing of glasses continued and is continuing

The tricky bit to explain, however, is the "j'ai quatre ans". 

Someone has made an attempt here: https://french.stackexchange.com/questions/31604/why-present-tense-in-depuis-que-je-suis-petite