Many years 作主语，谓语动词通常用复数，例如：
Many years have passed since they met each other last time. 自从他们上次见吗到现在已经过去很多年了（本句中，many years 作主语，谓语动词用了复数have passed.）
Mamy years were to pass before we met up again. 过了很多年我们才再度邂逅（摘自《网易有道词典》）（本句中，many yeats作主语，谓语动词用了复数were）
