Yeah years start at 0. But that's because it measures the offset from the beginning of the calendar. You can similarly expand this to all distance based measurements. But that is completely different from counting, which shouldn't be conflated with distances. People always say the first of some sequence and only people who care about 0-based indexing tries to spread the 0th of some sequence meme.

Which days are in a Month? You dont start with june 0th and end with june 29th?

I would if I could!

I may as well amuse myself here:

My ideal calendar has 12 30 day months, days 0 to 29.

If it's 10th June and you have an appointment for 0 August, that's 50 days from now.

At the end of the year, a 5 or 6 day 'month' called Holiday. 30th December becomes Christmas Day (observed) and 0 January is still New Years. New Years Eve is either 5 or 6 Holiday.

6 Holiday would be a lot of fun. ^_^