nothing new; same as always; not the first time
Fixed expression used to dismiss something as unsurprising or typical, often with a resigned or matter-of-fact tone. The negative form じゃない is colloquial; the more formal variant is 今に始まったことではない.
See also: 今に始まったことではない (いまにはじまったことではない)
It's nothing new for him to be late.
It's not the first time this shop has been crowded, you know.
Standard kanji spelling for this fixed expression.
Variant using 事 instead of こと; less common but still seen.
A fixed phrase composed of 今に (up to now), 始まった (started), こと (thing), and じゃない (is not). Literally 'it is not something that started now', meaning it has been happening for a long time.