I'm thinking he's 9 1/2 and maybe even 10 1/2
Brilliant story and great photos, but I'm thinking that first antler is from a 3 1/2 y.o. deer (and maybe a 4 1/2 y. o.) which makes this deer several years older. (The jump in size looks like the 3 1/2 to 4 1/2 jump sequence.) Not all deer produce large antlers however, regardless of age, and I've seen 6 1/2 y.o. Kansas whitetails with 130" antlers.
We killed a very distinctive 8 1/2 y.o. (4x4) buck on our place this year, have been seeing him ever year since he was a 3 1/2 y.o. and although he got a lot heavier, he didn't get much longer or wider. (And he stayed typical, with the same carry and conformation the whole while.)
Most deer in Iowa and Kansas don't go "down hill" until they are around 10. Their antlers will vary year to year due to injury and social pressure however.
It will not surprise me all to finally hear (read) that this deer was 10 1/2 this year.
What a wonderful story--you've done an awesome job documenting a stunning fragment of this deer's life.
Bronc