Great that you're thinking things through well, in advance.
If you look here https://www.englishforum.ch/education/ you will find, right at the top, several "sticky" threads which explain the Swiss education system well.
I think it depends on when your child's birthday is exactly, but my son and many of his friends began kindergarten when they were four years old (my son's birthday is in October). And keep in mind that kids usually or often go to kindergarten for two years here (or at least I think that applies to most cantons in Switzerland, but I'm not 100% sure).
Some parents do elect to have their kids begin kindergarten a year later than normal, I believe. But kindergartens here seem to be more focused on play than on teaching, so if your son missed the first year of kindergarten here, I would think or hope that wouldn't be a big deal.
As for those parents that elect topostpone kindergarten, do they still have 2 years of it?
I just guess my question is a bit opposite from what other parents usually seek here. Usually people ask here about how to put their child to kindergarten earlier than later, and I would vice versa postpone that to mitigate relocation stress.
Hence I'm especially interested in Zug since it seems to start everything one year later than other cantons. Still I'm not sure I understand things correctly and seeking for confirmation here. Also I wonder if there are other cantons that also start later.
I had to translate some of it from German into English via Google Translate, and this is what it translated to:
"All Zug municipalities offer a two-year kindergarten. The kindergarten year before the compulsory kindergarten is voluntary.
School entry
The kindergarten year before entering the 1st class of the primary level is mandatory. Entry to compulsory kindergarten is called school entry. The following age limits apply to this school entry: Children who are five years old by the end of February attend kindergarten the following school year. Children who are five years old by the end of May may attend compulsory kindergarten in the following school year."
So it looks like maybe the first year of kindergarten is optional but the second year is mandatory (though maybe I'm not understanding it correctly?). Maybe there are similar pages for other kantons as well.
Also bear in mind that kindergarden is likely to only be in the mornings with maybe one afternoon as well during the week. If both parents plan to work then you may need to juggle to cover childcare or arrange childcare during your work time.
You can pay for a hort (lunch and afternoon care) or use a private kindergarden. If you're paying for daycare, it's actually cheaper to put your kid in a couple of years of private schooling just to not have to worry about dealing with evening care and all the 13 weeks of holiday care.
We moved to Zurich in the March of the school year when my child was 5. The kindergarten start date we were given was about 6 weeks after we moved, so it didn't feel stressful after the relocation.
We could have waited until after the summer holidays for her to start as kindergarten wasn't compulsory back then but I'm glad we didn't. In those two months in kindergarten she made progress in learning German with 1 to 1 lessons, enjoyed going to the woods each week, did a day hike and a class trip to the zoo and started walking to kindergarten and back with a few of her classmates.
The teachers did a good job of settling her in and even starting out with zero German she had a lot of fun and was well integrated by the time she started school a year and half later.
The kids started when they had turned 5 by a certain date the previous year (so when my kid was 5 by April 30th 2018 she was automatically registered into the local kindski for that August 2018). Your Gemeinde will share those dates if you have any doubts.
Yes to latter question where we are in Zurich the 2 years of Kindski are mandatory.
The Cantons have not all harmonized their school systems. Those cantons which have joined the "Harmos" Concordat, will have similar starting dates for kindergarten and school those who haven't may have different ones ( https://de.wikipedia.org/wiki/HarmoS-Konkordat ). Zurich has joined. Zug has refused. Schwyz is apparently still pondering.
In Zurich you currently start Kindergarten if you have turned 4 years old by the 31 July of the respective year (The cut-off date has been shifted slowly to the current date of 31 July, which is my other posters may have had different cut-off dates. Also the English explanation in the link of OP's first post is slightly confusing since it mentions "will attend Kindergarten the following year", what is meant is not the following calendar year but the following school year, which starts in August).
We still go by cut-off date of December 31st, and start school on the Monday of the first week that has a Friday in September (it used to be first Monday in September).
And kindergarden is three years, though first year is now optional, and starts at 3.