Can't sync calendar between iMac and iPhone

Hallo, I have iMac (OS 10.8.5 Mountain Lion) with iTunes 11.1.3 and I am trying to sync Calendar with iPhone 5 (iOS 7.0.4) but sync doesn't work anymore. It seems the Calendar of Mac and Calendar of iPhone are not connected each other.

I tried also with iPad mini but same result: no sync anymore.

I tried many solutions but no solved the problem:

- delete/restore calendars of iMac Calendar

- select the Sync Calendar checkbox and tried to select one calendar at a time to see if it syncs

- reset OS X sync services: http://support.apple.com/kb/TS1627?viewlocale=en_US

- advanced troubleshooting for contact and calendar syncing: http://support.apple.com/kb/TS2481?viewlocale=en_US

Apps, OS X and iOS are uploaded and sync worked without problems until a short time ago (I think 2/3 days ago): don't know what happened.

More, in iTunes the Sync Mail checkbox is disable and it is no possible to activate it: in the past I could select mail accounts I wanted to sync, now there are no mail accounts in the box and the checkbox is disable (but it seems mails sync correctly... so don't understand why...).

I don't want to upgrade to OS X Mavericks and don't want to use iCloud (I tried it for calendars but Calendar crashes and for hours it stayed blocked).

Since that I tried with 2 different devices and sync doesn't work, I think it could be a problem of iTunes 11.1.3...

I know that with Mavericks sync of mail, calendars, etc. is possible only with iCloud but I don't have Mavericks installed so the problem maybe is not that.

Please, could you help?

Thanks in advance

G.