can i upload an old purchased DVD to itunes

Commercial DVDs cannot be uploaded to iTunes, unless you have the rights to a digital copy. Other uploading to iTunes would require doing illegal acts to the DVD to get them on the computer. That cannot be discussed here.

You would have had to buy not only the DVD, but it would have needed to come with the additional license of digital rights. 20 years ago that did not exist. Commercial movies those days contained copyright protection to prevent you from copying the device to a computer and sharing. When you purchase a DVD, you are really just purchasing the right to watch the movie, you do not "own" it. So you cannot just do what you wish with it. Now, when purchasing DVDs, many come with the additional download codes for the digital rights, so you can download it to iTunes and put it on mobile devices. I know that is a short explanation, it is all about copyright, but I hope it helps.

Depends on the content.

Music doesn't come in DVDs but on CDs

Movies have DRM which mostly copy protected.

You're welcome.

If you have a computer (Mac or Windows) with iTunes and DVD drives, you can transfer it onto them. If you have a computer with iTunes but no DVD drive, you can use remote disc

https://support.apple.com/en-us/HT203973