It's quite difficult to give you some help with not viewing and evaluating the data.
Thomas Keane, b abt 1869 in Ireland, correct?
He immigrated what year? Did he immigrated on his own or with parents/family?
Have you found a likely manifest for his arrival, I'm guessing he came into the port of NY? I realize that Thomas Keane is a common name, but this data is on-line in several sites, Ancestry included.
The 1910 and 1920 Census both cite his naturalization as 1889, is the correct?
He would have had to immigrate at least 5 years prior to first papers, that makes the math sketchy.
20 years old at naturalization, means a minimum of age 13 at immigration.
I'm going to encourage you to google and read. Here's some to get you started. http://www.genealogybranches.com/naturalization.html