As mentioned, the reason G/S are 40-50 while R/B are 50/60 is because of balance. I've never actually looked into it in-depth, but that's just how it turns up when you're ready for the E4. By the time I reached the Elite 4 in R/B, my pokemon were nearing or had reached the level of the E4's pokemon. And in G/S, yep they were all near or around level 40. I don't know whether there was just more trainers or Team rocket battles in R/B to advance from or what.
And about the level 60 Typholosion, I should ask what levels your other pokemon were. I always train my Pokemon in a balanced way, meaning all of them are usually the same level with my starter maybe 2-3 levels ahead. When I see people on message boards showing their teams, and it goes like "Level 64 Feraligatr, Level 22 Pidgeotto, Level 18 Rattata" and such, I cringe.