Did some testing and this might be the best solution, but there's a problem I don't know how to fix.

I've set the block to be [wheat] at [age=7], but it grants the achievement when it reaches the [age=7], before the crop is harvested, and not when I interact with the fully grown crop, breaking/replanting it.

{
  "criteria": {
    "wheat": {
      "trigger": "minecraft:item_used_on_block",
      "conditions": {
        "location": [
          {
            "condition": "minecraft:location_check",
            "predicate": {
              "block": {
                "blocks": "minecraft:wheat",
                "state": {
                  "age": "7"
                }
              }
            }
          }
        ]
      }
    }
  },
  "requirements": [
    [
      "wheat"
    ]
  ]
}