Before explaining what SEP is could you please tell me if you have medical insurance coverage under a group health plan based on your or your spouse's current employment?
No neither I nor my spouse have medical insurance coverage under a group health plan.
Unfortunately, no relevant information is found.
If the SEP applied to me at what age would I have to apply for Medicare Part B?
You would not have to apply for Medicare Part B at age 65.
At what age can I apply for Medicare online?
You would be able to apply for Medicare online when  you are at least 64 years and 9 months old.
What is the initial enrollment period?
Your initial enrollment period begins three months before your 65th birthday, includes the month you turn 65 and ends three months after your birthday.
Can  you please explain what happens to my application after I apply for benefits?