Step #4 Graduate High School / GED / College - Now at 17-18 years old is where your options start to open up.  You have to have a high school diploma to enlist.  Recently they have started to accept a GED certificate but depending upon your choice of service you may need a semester of college level classes to join the military.  You can enlist as young as 17 years old with the signature of a parent or guardian or you could decide to attend college for a few years or graduate.  Many SEAL enlisted are college graduates with advanced degrees even.  So after college you can either enlist, join as an officer by attending OCS - Officer Candidate School OR you could get a military scholarship and attend college for free by joining an ROTC college or the U.S. Naval Academy.  All sources can lead to attending BUDS as an officer.  This will also give you four more years to REALLY train hard as well.

Also read - How to Get to BUDS for more information on the recruiting side and your options.

*NOTE - Do I even need to say stay away from drugs and alcohol as it has no purpose in this training.  Do not get a criminal record or DUI / DWI !!!!!! 

Step#5 - If You Choose to Enlist - There are many opportunities for the enlisted SEAL or Special Ops soldier.  Not only will you receive some of the best training in the world, but you can also earn thousands of dollars in bonuses.  But, when you meet the recruiter you will be assigned a SEAL mentor once you have signed in.  SEAL Mentors are former SEALs / Special Ops who help you properly prepare for the training you have signed to do.  You have to sign up with the Delayed Entry Program to meet with the SEAL Mentor and do the workouts.  You will not sign up at first as a SO - Special Operator - you have to pass the BUDS Physical Screening Test (PST) first before you can be part of the SEAL Challenge Program.  This means you have to pick another Navy designation when you join, but that goes away after to pass the PST. 

Step #6 - Acing the PST - You want to go to Boot Camp in the best shape of your life.  Do not think the Navy is going to get you in SEAL shape during Boot Camp.  You need that foundation NOW and hopefully after a lifetime of fitness and athletics you will have the ability to build on that foundation.  This means you need the following scores on the PST to have about an 80% chance of graduating BUDS. 

Swim 500yds (side, breast or CSS stroke) in under 9:00                ( sub 8:00 for officers)*
80-100 pushups in 2:00                                                                 (100+ for officers)* 
80-100 situps in 2:00                                                                     (100+ for officers)*
15-20 pullups                                                                                (20+ for officers)*
1.5 mile run in 9 minutes                                                           (sub 9:00 for officers)*

* Officer billets are much more competitive and require higher scores to be accepted generally.  This is because there are 80% more enlisted than officers.

For the enlisted, the good news is that you get some pre-training after Boot Camp which is run by SEAL instructors in Great Lakes.  There you get to workout and get back into shape after losing some of it due to Boot Camp schedule.  This program is designed to better prepare you for SEAL training and it is tough.  If you can get into above average shape prior to Boot Camp and use that time as a taper, then you will be in perfect shape to start ramping up for BUDS again after Boot Camp.  However, I recommend within at least 4-6 months of attending Boot Camp you should be running in boots and swimming in fins.  Same for officer candidates.