You can claim prior years' property tax in the tax year you paid them. For example, if you paid your 2018 property taxes in 2019, claim them on your 2019 taxes. However, you can't include any late fees, interest, or penalties – just the tax itself.
Starting with tax year 2017, you can still claim prepaid property tax but only if it was also assessed in the tax year you're attempting to claim it.
In other words, if your local assessor sent you the 2020 property tax bill in 2019, and you paid it by December 31 of 2019, you can claim it on your 2019 return.
However, if you didn't get an assessment for your 2020 property tax, but you went ahead and paid it anyway by the end of 2019, you can't claim it on your 2019 taxes (but you could on your 2020 taxes, assuming you get assessed in 2020).