You can try something like
Code:
SELECT ... FROM table1 t1 INNER JOIN table1 t2 ON t2.LastName = t1.LastName AND t2.BirthYear BETWEEN t1.BirthYear-5 AND t1.BirthYear+5 ...
This returns persons present in both tables (all persons not present in both tables are left out). When one table is more presentable compared with other, then you have to use LEFT JOIN instead of INNER JOIN. For people not found in 2nd table all fields from 2nd table will then be Null.
And relying only on birth year will probably give a lot of wrong info - there must be something other used to link tables too (e.g. last name in my example)