What's the number of years that a representative must have been a citizen?

A member of the U.S. House of Representatives must be a U.S. citizen for at least seven years. The other requirement for being a House representative is that the member is at least 25 years old.

The citizenship clause was meant by the Founding Fathers to encourage immigrants to participate in government. This also meant that elected representatives could be a reflection of the constituencies that they served. However, the Founding Fathers also wanted to prevent foreign interference in American government affairs, hence the citizenship requirement. By comparison, England at the time required members of the British Commons to be natural-born citizens to hold office.