It's hard to say...
Mine were pee pad trained and I introduced the grass last year when they were 3.5 yrs old. Roxy LOVES it as she is my MAD MARKER (outside) - this grass inside is such a TREAT for her (go figure). TJ still isn't sold on it. Although, he walks kinds funny on real grass too, so maybe he just doesn't care for any grass feel.
You can search online and just get a piece of clearance or odd cut pieces of doggie turf for cheap if you are just going to use it outside in the winter
