Passé composé vs present with depuis que

Question

Please clarify why in this lesson  the passé composé is used in "Depuis que je t'ai rencontré, ma vie a complètement changé"  but present tense is used in "Depuis que j'ai quatre ans, je porte des lunettes."   Thanks.

Accepted Answer

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

Answer

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