At both the ends of MGS1 and MGS2 they always seem to talk about humanities only concern with passing on their genes. Obviously genes play a large role in the MGS series (Genome Army, The 3 Snakes, Trying to find the "Soldiers Genes", etc. etc.) but, why do they always seem to hit you with this totally random crap at the end of the games? And also, is Solidus a clone of Big Boss or his true son?

Exactly what do you mean "random bullcrap"? A lot of the themes, philosophies, and ideas presented in the stories may seem confusing but all are relevant to the central theme of each game. It's just that all of the themes, philosophies, and ideas in the game collide in one gigantically confusing explosion at the end of the games.

It just takes some critical thinking to figure out just what the hell Kojima is trying to say.

As for Solidus, he is a clone of BigBoss just like Solid and Liquid. Unlike Solid and Liquid who only received one type of BB's genes (recessive and dominant), Solidus received and equal amount of recessive and dominant genes. Because of this, Solidus suffered an advanced aging mutation that caused his body to age must faster than it should have. That's why he looks so old.