Board Thread:General Discussion/@comment-4458546-20130808000528/@comment-50.53.154.87-20130809124426

I think something that's considered very noteworthy has been almost entirely overlooked amidst the current speculation about Solidus (particularly his age) -- the secret phone call at the end of Peace Walker.

Kaz asks Zero about "the sons"; he responds to Zero's answer with "Two already... Really..."

The "two already" are obviously Liquid and Solid, meaning Solidus hadn't been born yet (or before 1974, at least).