years old是固定搭配，表示…岁，前面通常是数字。

是个形容词短语，多用作表语。year根据数字选择用单数或复数，即大于一的数字时，year须用复数。如，Heis10yerasold.他十岁了。Mark didn't shape up until he was thirty years old. 马克到三十岁时才振奋起来。This fossil may be over 2 million years old.这化石可能超过二百万年了。