Basically what Jetlaggy said. The pension has been set up using actuarial data to ensure that “on average”, no matter what pension option you take for a given number of years of work, you will receive the same number of dollars in retirement. It can get complicated fast dealing with survivor benefits, a guaranteed payout term, etc. You can start receiving pension benefits at 55, but they account for the five “extra” years you are likely to collect (plus extended lifespan of retiring young) by reducing your benefit. Most guys who go before 60 live off savings until 60 to avoid this.

The actual biggest obstacle to retirement at 55 is I don’t believe you can access your 401k and B plan money until 57.5 years old. Otherwise, a twenty year career is more than enough time to retire independently wealthy (not rich).