No, a 70-year-old father cannot be claimed as a dependent by his son on his taxes. To be eligible to be claimed as a dependent on someone else's taxes, the person must be a qualifying child or a qualifying relative. The person must meet certain criteria, including:
Must be a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico.
Must not have provided more than half of their own support during the tax year.
Must not have earned more than the applicable dependency exemption amount, which for 2021 is $4,000.
Must not be claimed as a dependent by someone else.
A 70-year-old father is not considered a qualifying child and may or may not meet the criteria to be considered a qualifying relative, but since he is not a qualifying child, he cannot be claimed as a dependent by his son on his taxes.