I will answer this question the way I have answered it any other time.
DD was 5 years old on our first trip. We did not take a stroller for her, but we eventually rented one on the third or fourth day of the trip. Even still, she did not ride in it the whole day. It was more of a backup for the end of the day because the rest of us did not want to take breaks or go back to the room.
Fast forward to now. DS just turned 8. He is autistic, has sensory issues, low muscle tone, low stamina, and he is generally very "clunky" on his feet. We are planning on renting a double stroller at Disney for him next week when we are there. I know he is "too old" for a stroller. I know people will look at me with condescension for my choice because they don't know he has an invisible disability. I don't really care. He is my kid and I know what he needs in order to have an enjoyable trip.
My point is, all kids are different. Just because Mrs. Smith's 4 year old can tour the parks in true commando fashion with no stroller doesn't mean Mrs. Jones's 6 year old can do the same. If it turns out that your 8 year old needs a stroller, you put that 8 year old in a stroller and do it with a smile!
Have a great trip.