This is a topic we discussed in detail last year. I take it your son will be 8/U Heavyweight? If so, during regular season, some of the smaller tournaments they will allow a bracket of heavyweight that is from 96-whatever. (I believe 95 is the top weight division in 8/U.)
When you get to the bigger tournaments, sub-districts, districts and state, there is a 25 pound max difference. They put the 25 pound difference because if they set it at 5-10 pounds, they probably wouldn't have many kids to wrestle through out the year. Sometimes there will be just one kid who has no one else to wrestle and they will put them in the next bracket down.
My son last year wrestled a kid that was 45 pounds heavier and many that were 25-30. Tell him don't give up, he can do it.