How would you find an Asset ID via a script?

One method of doing this would be to loop through all the Hat objects that a player is wearing. Inside each hat, there should be a Part called "Handle" which contains a Mesh object inside of it. You can read the MeshId or the TextureId properties of this Mesh object to find the AssetId of the hat.

(Keep in mind, however, that ROBLOX is currently transitioning into turning Hat objects into Accessory objects.)

Now, first, let's look at the MeshId (you could use its TextureId if you want, but for my example, I'm using MeshId). MeshId is a property that holds a String something like this:

"rbxassetid://190770123"

However, we want just the numbers at the end, not the String. To do so, we would need to do utilize the match function for strings.

Here's how to do it:

-- New player enters the game
game.Players.PlayerAdded:connect(function(player) 
    -- The player's character loads/reloads
    player.CharacterAdded:connect(function(character)
        wait(1) -- Waits a second to allow accessories to load
        -- Loops through all the contents of the character
        -- Looks for any "Accessory" items
        for i, v in pairs(character:GetChildren()) do
            if v:IsA("Accessory") then -- We're only looking for Accessories
                local asset = v.Handle.Mesh.MeshId

                -- This is how to get only the numbers from the String
                local assetId = tonumber(asset:match("%d+"))
            end
        end
    end)
end)

Now comes the part where we need to see if the Accessory is from 2007 or not. If it isn't, we need to get rid of it. To do so, we need to use MarketplaceService.

Here's what the final script should look like after using MarketplaceService:

local marketplaceService = game:GetService("MarketplaceService")

-- New player enters the game
game.Players.PlayerAdded:connect(function(player) 
    -- The player's character loads/reloads
    player.CharacterAdded:connect(function(character)
        wait(1) -- Waits a second to allow accessories to load
        -- Loops through all the contents of the character
        -- Looks for any "Accessory" items
        for i, v in pairs(character:GetChildren()) do
            if v:IsA("Accessory") then -- We're only looking for Accessories
                local asset = v.Handle.Mesh.MeshId

                -- This is how to get only the numbers from the String
                local assetId = tonumber(asset:match("%d+"))

                -- Gets all the product information from the assetId
                local info = marketplaceService:GetProductInfo(assetId)

                -- Checks to see if the creation date is 2007 or not
                if string.sub(info.Created, 1, 4) ~= "2007" then
                    v:Destroy() -- Destroys accessory if not
                end
            end
        end
    end)
end)

Hope this helps! if it does, don't forget to click Accept Answer and +1 my Rep!