I have a friend with a possible dilemna regarding his military service.

The details provided to me are the following:   

My friend, let's call him John, was awarded a Secret clearance at age 18 after joining the military.  While possessing a Secret clearance John made some foolish choices.  John confided that he very stupidly used pot (5x) and E (9x) over a 2.5 year period as well as abusing prescription drugs on a few occasions, during that period.

John has since been commissioned and some of the tail end his misconduct may have occured during the beginning of his commissioned career, but mostly while in the pre-commissioning program.

For the last several years, John has had no contact with any drugs and has declared his resolve never to again.  John rarely drinks either.   

Although John was never exposed to Secret information while possessing a clearance, his Secret clearance was necessary to remain commissioned and was awarded prior to commissioning.

John is now in a position to move into the intelligence community as part of the military or remain in his current community, completely unrelated to intel.  The intel community position would require a TS/SCI.  He also could resign his commission and work in the private sector.  His concerns which brought him to me are the following:

1.  Will he need to fill out a new SF-86 when his Security clearance reaches the 10 year mark?

2.  He has no intent to falsify the SF-86, so he would have to check yes on part 24, A and B.  Can or will that information be shared with his branch, since he would have admitted to those offenses being committed while in the military or will his organization only care if he is cleared or not?  If so, can he be NJP'ed or administratively discharged (non-punitive) as a result? 

3.  Is it likely that John's current Secret clearance would be revoked due to his disclosing the offenses while applying to for the TS/SCI? 

4.  Is there a statute of limitations for substance abuse?  If so, does that prevent a medical or admin discharge too?

For different reasons, he and I both would appreciate any accurate information about this.  Thank you.