数世纪以来的英文

应该是： since the seventeenth century英语世纪年代前面必须加the。如： the 1990's=the 1990s; since the twenty centry

since 8 centuries

since the 21th century

Since more than one century

since 8 centuries ago

for over a century

It had been more than a century since....

from the 21st centry