Yes your Greyhound is a 45 mile per hour couch potatoe. However that does not have to stop you from getting out and about with your fast friend and having some quality time together.
Here are just a few suggestions:
Yes you can teach a dog of any age new tricks. How about agility and obedience training?
For socialable Greyhounds help those in need by becoming a Therapy dog
Meet other like minded folks at a Greyhound Gathering.
How about meeting other hounds for a weekend walk in the park?