APC on their airline profiles gives you a breakdown of each Airlines retirement benefits.
A plan - Traditional defined benefit plan. FDX will pay 2% times Years of Service (YOS) (Max 25 Years) times average of your high 5 (Max of 260k). So a top defined benefit of 130k. 18 YOS could get you about 94k for life. This benefit may or may not get better. In 20 years what will 94k be worth? UPS has a different scheme to get you similar numbers at 30 years. At 18 YOS UPS would get you about 75k.
B Plan. Max of about 20 (FDX) to 30k (ups) invested per year in your name funded by the company. Contributions are a percentage of pay, FDX's will be 9%, UPS will be 12 or 14%. Again this is in addition to your normal pay and is not reported as income.
Most companies have 401ks where you put money aside, after a couple of years, particularly with a mil retirement, it is easy to max this out. FDX matches only $500 a year.
Sick leave buy back. This is paid to those who don't use their sick days every year. At FDX this is 72 hours a year (about a month of flying). once your sick bank hits 650 hours or so, FDX will buy any extra hours at the end of the year and put it in your B Fund bank. If your b fund bank is maxed out you get the cash.
The 401k and Bfund contributions are currently limited to about $55k total per year by the IRS.
Bottomline, the sooner you start your second career the better your retirement will be when you hit 65. Regardless of who you go with. I am no expert but you should have the hours to be competitive now. Pay an expert and take the first job at United, Delta, American, SW, UPS, Alaska, or Fedex you get offered and start building retirement.