I honestly thought Oli and Richard were the oldest Rammstein members for years! I only learned recently they weren't and I'm shock!
It would be interesting to know why you thought Oliver and Richard were the oldest! But yes, the two of them are the two youngest Rammstein members. Richard was born in 1967, so only one year after Schneider and Flake, while Oliver is the Rammstein "baby", four years younger than Richard, and the only member born in the 70s.
I guess age didn't matter that much when they met back in East Germany music scene...
Flake and Paul first met at Flake's second rehearsal with Feeling B (the first one where they actually played, as the time before they just got drunk). Paul arrived before Flake was drunk, and was very surprised when he saw a young student-like guy opening the door for him. Flake, on the other hand, stared straight at a man with short hair in front, long in the back, and a moustache.
The two of them met Till while they were in Schwerin with Feeling B. They more or less barged into his place one night when all the pubs were closed, and turned his house upside down.
Till, the oldest Rammstein member, noticed Richard, the second youngest, because Richard's hairdo reminded him of a chipmunk. Richard met Paul and Flake through Till.
Schneider first saw Feeling B in 1983, when he was an apprentice in communications engineering where Paul was one year further along, but he only knew Paul by sight. He had, as the only Rammstein member, joined the army, but he came back in 1988 with a powerful hatred of the army, the GDR, and socialism. That was when he started looking for cool people in the underground scene. Schneider met Paul through Die Firma, and from that, he went on to play in Feeling B. Flake he had known for a while through other musicians.
Oliver, the youngest Rammstein member, didn't start playing an instrument until he was 19, when he started playing classical guitar. He didn't know many other musicians and felt a bit lonely until he met Richard, and the two of them played classical guitar together every Sunday. It is natural to assume that Oliver met the other musicians through Richard.
This long answer may not exactly be what you were looking for, but your question triggered a train of thought and I find Rammstein history really interesting - all these coincidences that led to the creation of this band that we love so much...