For my part, I do not castrate (which is the correct term) any males until they are a
t least 6 mnths old, mostly because 1) whyever do it earlier with all the risks involved in subjecting a very young, low bodyweight cat to sedation, anaesthesia and (medically) unnecessary surgery, 2) I like the males to develop so you can see they are males.
Vaccinating at the same time as sedating/anaesthesising is incredibly dangerous: the sedative will hide any immediate allergic reaction to the vaccine leaving it a tad late to do anything sensible about it, as well as adding another (unnecessary) stressor.
Risk perception: ketamine is dangerous, but early, unnecessary surgery isn't?
One of my favourite rants!

Per