There are 23 years between 1988 and 2011.
4006
1788/365= about 4.9 yrs
224 years
25
24
Including 1988 itself, there were 7 of them. They were 1988, 1992, 1996, 2000, 2004, 2008 and 2012.
There were 5 years between 1977 and 1998. They were 1980, 1984, 1988, 1992, and 1996.
June 21 1788
Zero
That depends on exactly what you mean by "between": if you want the number of whole years that are after 1988 but before 1999, that's 10 (1989, 90, 91, 92, 93, 94, 95, 96, 97, 98). If you want the number of years between, say, April 5, 1988, and April 5, 1999, that's 11.
That depends on the make, but not likely with that many years in between.