How long do you keep Tricare after you get out of the military?

1. No
2. At 60
3. Right then
Everyone is Medicare at 65 and whatever you have becomes secondary, hence the shift to Tricare for life. Why pay for something else? BTW choose wisely over Standard and so called Prime. If you live near a MIL medical facility and don't have anything better to do than deal with no parking, waiting for hours, and being required to pay for it, by all means go for it. If you want to live a more normal life, take the money you would have paid for Prime and that becomes your copay pool. Need serious surgery that requires a chunk of money? You can still go to the MIL hospital. No MIL hospital but VA is nearby? You can go there. They bill Tricare. Never could figure out why I'd pay money to be forced to go to a MIL provider to get a referral to the outside. I pay my $20 on Tuesday out here in the sticks to get the referral to see the pro in Coeur 'd Alene on Friday. Have to drive anyways. Oh, if you live out in the sticks, the one time payment for Life Flight coverage is a good idea.

One active retirement, you and family have it til you go on Medicare, then it becomes Tricare for Life as a Medicare supplement. My wife became (Social Security) disabled in her late 50's and had to go on Medicare by the laws. We were upset at first, but it has been good as we almost never see a bill. (And she has lots of Med procedures). What medicare does pay TFL picks up.

There are various TRICARE Health and Dental plans that one can be eligible for. Once you leave the military, if you are not eligible for one of the transitional plans, 99% have eligibility for the Continued Health Care Benefit Program. The premiums are (in my opinion) high. There are so many variables for eligibility, the three basic scenarios you provided are not enough individual info to determine TRICARE eligibility.
1. ETS/resign commission - need to know duty status, voluntary/involuntary, adverse actions, etc.
2. Reserve retirement - before age 60 - you have TRICARE Retired Reserve and TRICARE for Retirees.
3. Active retirement - regular retirement, non-regular - i.e. medical. less than 20 AFS . .
BLUF: non of the above matters if your DEERS is not coded/updated correctly. Your information in DEERS is going to drive what benefits you are eligible to receive.