Generally aging aircraft are limited by the manufacturer and local aviation administrations. These limitations are most usually based on noise production (by country) and structual expectations (by manufaturer). I have not heard of any general age limitations (especially Russia given the age of the aircraft they operate).
China is in the works of producing their own aircraft but the production and delivery of these aircraft is not in the near future. In the E.U. Airbus has driven CAT4 noise abatement limiting the usage of older Boeing and MDC aircraft operations.
What you have heard does not hold weight in my oppinion in the global market W/O further detail.