So basically I have a scyther and I want to evolve it but am I able to still train it in gen 1 once it is a scizor?
Did you get your Scyther from the wilderness? If yes, then no, I tried evolving slowpoke to Slowking in Gen 1 and beat a few Pokemon with it and it didn't receive any exp. If it's from an egg, it's highly still be able to be trained after evolving. If it's from a trade that's originally from an egg, then it's supposed to be the same as above.
Also if you're lvl 50 non of the rule I stated apply. You can train your generation 2 pokemon in generation 1 region.