We present the results of multi-epoch global VLBI observations of the Compact Symmetric Object ( CSO ) , 0710+439 at 5 GHz .
Analysis of data spread over 13 years shows strong evidence for an increase in the separation of the outer components at a rate of 0.251 \pm 0.029 h ^ { -1 } c .
Dividing the overall size of 86.8 h ^ { -1 } pc by this separation rate implies an estimated kinematic age of only 1100 \pm 100 yrs .
After taking into account possible temporal variations in hotspot advance speeds due to cloud collisions or hydrodynamic instabilities we argue that the upper limit to the age of 0710+439 is most likely within a factor of 2 of this estimate and certainly within a factor of 10 ( i.e . < 11 000 yrs ) .
This result therefore strongly supports the idea that Compact Symmetric Objects are very young radio-loud sources .
Furthermore the large radiative efficiency we calculate for 0710+439 is consistent with strong negative luminosity evolution as CSOs grow in size and with them evolving into classical double sources .