"Brief and casual absence" should not interrupt continuity during the 5 years in question. Don't forget 2 of the years will have to have occurred after your 14th birthday. You should double-check in person with an immigration attorney if you had frequent travels during the period in question.
This advice does not form an attorney-client relationship and is merely informative. It should not by itself be relied upon to address a legal concern.
The five years physical presence requirement refers to the years you spent (or did not spend)i in the US during your adolescent years; does not concern itself with the present. You can obtain the documentary proof therefor by retrieving your school records, medical visit, vaccination records, taxes, etc.
Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.