A lifelong commitment is one that lasts for someone's entire life.
You hear people talk about making lifelong friends or having a lifelong passion. This means that these things are with them from young adulthood until old age. A lifelong job, on the other hand, could be one where someone stays in the same profession their whole life. Some hobbies can become lifelong, too - for example, playing music or painting. In general, the word 'lifelong' is used to describe activities, relationships, or goals that have no end date and are meant to continue indefinitely.
Extending for the entire duration of life.
Example: They were lifelong friends; they met in elementary school and ended their lives in the same rest home.
