Sometimes ancestors are elusive. Robert Anderson, from Scotland, is either just elusive, or a perennial liar. Based on various documents, here is his age and likely Date of Birth. While he has a common name, these documents are likely to be him because of the names and places of birth for family members and because he’s listed in Brooklyn Directories, starting 1864, as a machinist. He lives in a narrow area, all homes within a few blocks of one another.

Source
1860 US census
1863 Draft
1870 US census
1880 US census
1892 NY State census
1900 US census
Age
Age 46
Age 44
Age 60
Age 62
Age 70
Age 84 b. Dec 1815
Year of Birth
1814
1819
1810
1818
1822
1815
The date that seems most believable is the 1900 census, when a specific month and year is given.
The least believable age is the 1870 census, where he has aged 14 years from 1860, or 16 years from 1863. However, he then only ages 2 years from 1870 to 1880. The 1892 date is also odd as it doesn’t work well with either the 1880 or 1892 dates.
We know that one source of date issues in census records is that the person reporting information may not have good knowledge.
If we assume a birth date of 1815 date, things look much more sensible.However, it could still be a year or two in eaither direction.
Date
1860 – 45
1863 – 48
1870 – 55
1880 – 65
1892 – 77
1900 – 85
Next steps – Try to find immigrants named Robert T. Anderson.
In the 1900 census, he claims he immigrated in 1850, but since his first child is born in 1843, that seems unlikely!