What age is recommended for puppies to use an exercise pen in the house? Our 18 week old puppy is lunging and biting us.

There is no age that is too old. If it makes you feel better my young dog is now almost 16 months and we still use the expen at times. I've had pups that didn't need it past 6 months but it's always better to use it if you need to.

I feel that puppies do best when they have a place to decompress in the house where we aren't constantly having to correct them or micromanage them. With the expen they still are in the family environment but it's just better for everyone long term. I even use the expen for my adult dogs occasionally, when we travel or have non-dog people over to our home and I don't want to put them in a crate.