Veetans live (tops) around 25 years, but begin their grand "walk-abouts" around 3 or 4. So Nosh's grandfather has about 22 years of space travel behind him.
The current emperor, Fernando's uncle, and the one we've met in the strip, has only been in power for a few months.
The previous emperor, Fernando's grandfather, was the one the elder Veetan served under.