I am 23 yrs old.

I have two questions:

1. Is there an age limit for ROTC, if you wish to go through ROTC in order to become an Officer in the Marine Corps? For example, I just started college, as I said I am 23, I will not graduate until I am 27. What are my chances of becomming an Officer in the Marine Corps? Can I still go the ROTC route?

2. What is the difference between going through ROTC while in college and joining the service as an Officer, vs. If one already has their 4yr degree? If one already has their 4yr degree can they go straight to Officer training and be an Officer, or is going through ROTC, the only way to guarantee that you can become an Officer in the Marine Corps?

Look up the age limits yourself: https://www.nrotc.navy.mil.

If you already have a degree though you can apply to OCS right now.

1. Age: "Be 17 years of age by September 1st of the year starting college and less than 23 years of age on June 30th of that year. Applicants must not have reached their 27th birthday by June 30th of the year in which college graduation and commissioning are anticipated."
2. Yes, you may go through officer training after you receive your degree. Be aware that there may be age limits for this as well.