I haven't had a puppy in years and plan on going to a show with a supported entry and sweeps. I don't see the age limit for the sweeps. My boy really won't be a puppy at 17 months old--does it go to 18 months?

6 months to under 18 months.

Depending on how big the show is Sweeps is broken down into:

6-9 months
9-12 months
12-15 months
15-18 months

Those are the traditional ages for Lab shows, but always read the premium list. Sometimes it might vary. Many breeds only go to 12 months, and if it's an all-breed sweeps you might see that.