I prefer doing the job on a still wet calf at birth, and banding it.
But you can cut a 7 month old calf easily enough. I've seen people cut the bottom of the scrotum off and squeeze each testicle down until you can get a good grip to stretch it. Then use the knife to scrape the attachment, fraying it so it won't bleed as much. I prefer slicing the back of the scrotum but in hot weather slicing the bottom off may be better.
You can also clamp the vas deferens and blood vessels, and your vet probably has the tool. I know vets that loan them to their customers. No blood, no fly problems, and easy to use if you can immobilize the calf. It's just like using a bolt cutter.