Gwendolyn: Table B25045 provides the number of SENIOR HOUSEHOLDERS with 0, 1, 2, 3, etc, vehicles in the household. The 18,013 is an estimate of senior households, not all persons age 65+ with zero vehicles in the household. It's a conservative estimate of the number of car-free seniors.
I ran the analysis through the IPUMS USA for the 2016-2020 ACS PUMS, and came up with 18, 636 senior households (comparable to the 18,013 from census.data.gov) with 21,429 seniors (65+) residing in households with zero vehicles.
To complicate matters you could look at car-insufficient households, say, a household with two working adults who commute by auto to work; one or more persons age 65+ living in that household; but only two vehicles in that household. In that case, the older person lives in a household WITH vehicles, but doesn't have access to a car when the working age adults are commuting to work by car. They're potentially isolated.
I would still stick with the Table B25045 analysis, because you can analyze the data at a county and census tract-of-residence level. Where are those 18,000 car-free senior households in New Mexico?