Most of us know this but for those that don't . . .

Age of Tire (How old is a tire?)

Check the sidewall for the date stamp, a four-digit code inside a rectangular box.  These indicate the week of the year, and then the year, that your tire first popped out of the mold. So a date stamp of “4012” would read as “the 40th week of 2012,” or some time in early October of 2012.

Prior to 2000, it was a 3-digit code: 2-digit week + year of that decade. Example "408" would be the 40th week of 1998 (or maybe 1997).

NOTE:  Many new motorcycles have tires that are up to 18 months old.  I believe this is the max allowed by law.  So, if you buy a bike that has been sitting on the dealer's showroom floor for two years, the tires could already be 3.5 years old.

Look for the word DOT on the sidewall of the  tire..It will appear on just one sidewall.  Following DOT will be a series of alpha or numerical symbols the last four of which are the week of the year and then the year of manufacture....For example, 2219 is the 22nd week of 2019.  I believe
DOT stands for Department Of Transportation, but that is just a guess.

Don't know the answers to other questions.