Does anyone know that if you childmind children over 8 years old, will you be inspected by Ofsted?

Not normally - unless there is a problem /complaint and then your documentation and working practices will be checked against the statutory requirements of the Childcare Register -

Ofsted | Factsheet: childcare - Requirements for the Childcare Register: childminders and home childcarers (http://www.ofsted.gov.uk/resources/factsheet-childcare-requirements-for-childcare-register-childminders-and-home-childcarers)

Hth :D