My understanding based on my research on the USCG website is that the only way you can go to DEPOT before you turn 27 is if you have prior military experience.
DEPOT (Direct Entry Petty Officer Training) is the actual initial entry training (3 week boot camp).
There are three enlistment programs that will qualify you to attend DEPOT as opposed to traditional 8 week boot camp. The programs are:
1. Direct Entry Petty Officer Program (DEPOP)- this is the program that allows you to attend DEPOT and enter as an E-4 or above if you have training and experience in a job that directly translates to a USCG job rating. This allows you to bypass having to go to an A-school if you enter the coast guard under a contract to do the job you have civilian experience in. You have to be between 27-40 years old.
2. Direct Entry Education Program (DEEP)- this program allows you to attend DEPOT training and enter as an E-3, if you have 60 or more college credits. Again, You must be between 27-40 years old.
3. Prior Military Service Program- this program allows you to go to DEPOT training and enter as an E-4, bypassing A-School. I’m pretty sure the rank and A-school waiver only apply though if you left another branch with that rank or higher, come into the USCG to do a rating that is the equivalent of your previous military job. I.E. if you were an E-4 Boatswains mate in the navy, you could enlist in the USCG as a BM, go to DEPOT, graduate as an E-4 and bypass USCG BM A-school. On the other hand if for example you left the army as an E-5 truck driver (88M) and wanted to be an ME in the USCG, you could still go to DEPOT, but you would only graduate as an E-3 and you would have to go to ME A-school in order to get E-4). There is no minimum age listed for prior military service applicants, just a maximum of 40.
So, based on what the original poster has told us about themselves, and what the USCG published, I don’t see how OP could qualify go to DEPOT. Of course I’m no expert , this is just what I’ve found from researching and talking to recruiters. For what it’s worth I’ve seen some rare posts on these forums mentioning people under 27 attending DEPOT without prior military service, so either that happened in the past when they may have had different age requirements, or perhaps they got some sort of waiver to attend while below the minimum age.