How to find date gaps between rows?

[Winnie]

Please help me with some idea for my difficulty of
finding the date gaps (by days) between unknown of number
of rows in the same column for each concatenation
of "LastName + FirstName + DOB" as a unique identifier?
For each "LastName + FirstName + DOB", there are one or
two or many plans (unknown number of start and end dates
for each person) with different "StartDate" and "EndDate"
columns. For example:

LastName FirstName DOB
PlanType StartDate EndDate Gap#
GapDays
AAA aaa 1/1/2000 A
1/1/2000 3/31/2000
AAA aaa 1/1/2000 B
4/5/2000 5/31/2000

BBB bbb 2/2/1950 B
1/15/1999 12/20/2002

Please advise how to get the gaps between each plan when
finish for each person and then put the number of gaps
into a column "Gap#" and the date difference by days into
another column "GapDays", If "Gap#" >= 2 for "LastName +
FirstName + DOB", delete; if "Gap#" <= 1 while "GapDays"

45, delete; then do the same thing for next person and

so on.

Thank you for kind help.

Winnie Zhou