I’d check the manufacture date on the sidewall of the tyres currently on to check how old regardless of wear. Thumbs up from me for Costco for tyres. Choice is a very personal thing - I like Michelin pilot sport on Both NC and ND’s - not a fan of the OE Bridgestones, also had Kumho in the past - personally prefer Michelin if pushed to choose.
I had the tyres fitted brand new within 3 days of collecting the car - a take in itself, so they’re well within date.
Good to hear a recommendation for Costco though. I was going to visit with my previous 2 cars but ended up changing the cars instead !