The age you disbud is determined by the rate of horn growth. Some you have to burn almost as soon as they are born, others you can wait up to 2 weeks.
When you feel little nubs they are ready to disbud. You don't want to wait till they are visible. At that point the horn bud has attached itself to the head and it is harder to stop the growth. Bucklings tend to have a wider horn base then doelings so doing them sooner is best.
I have a rheinhart X30 with a 1/2 inch tip.
A disbudding box is so helpful for keeping kids still during the procedure.
Here are some pictures of how I disbud.
First you shave the area so you can see how wide the base is and so you don't have that nasty smell of burning hair.
Next you place the disbudding tool over the buds for aprox 10-15 seconds - roll the iron around in a circular motion to be sure you get even pressure all the way around. Burn till you see a good copper ring and then the white of the skull.
This is how a correctly burned horn bud should look (I also sometimes take that cap off the tip of the horn bud - reduces the chance of infection.
IF this is how your burn looks then its not done correctly - below
when caps are removed - some will spray with blu-kote after this. I choose not to so I can see if its oozing or other issues. I feel spraying it will mask those issues and it takes longer for me to notice them.
Here is a video - be forwarned the kid is screaming in this video
I then comfort the kid for a bit and either give a bottle (of a bottle kid) or return him back to his mother butt first. Why the butt? so that she doesn't reject him because of the burn smell. Doesnt' happen often but it can. She may not totaly reject the kid but for a couple hours refuse to nurse the kid. Best to avoid this if possible.