You trust a page that has a picture of a Hydrocynus brevis as the picture illustrating forskahlii to give you accurate info on them? You trust a page that lists six species of AFT (somonorum) to give you accurate info when somonorum was shown in 1986 to be a junior synonym of brevis?
Maximum recorded age means little. It also doesn't mean that its the same fish as the one that was two feet long.
You're spouting off dated advice about this genus in a haphazard, careless manner that will result in someone making grievous errors in their fishkeeping if they attempt to follow it. African tiger fish are a painfully slow growing genus. With the fastest growing species, goliath, you'll get mean growth of less than a foot a year over a period of several years. Even goliath takes four to five years to achieve two feet. Forskahlii will take a similar period of time to have a real hope of getting over a foot. While not ideal, if the tank is set up correctly, a foot long ATF could certainly survive in a 70 gallon tank for some time. When in a properly set up tank, tigerfish are surprisingly sedate animals.