Well since Go made it's appearance in 2009 and C# in 2000, I wouldn't call that 'only slightly older', not even by programming language standards.
Beyond that, Go certainly doesn't have the same backing from Google as C# had from Microsoft, on the other hand Microsoft had a monetary incentive to provide support and tools/frameworks as they charged for those proprietary implementations while Google is giving Go away under a permissive licence.
Anyway, for fun I looked at the language poll made here recently on HN and compared C# and Go:
C# 1130 likes, 465 dislikes
Go 1126 likes, 365 dislikes
