Will RE Thunderbird or Classic suit me? I am 5'8" and 53 kg..

Wear a bikers' jacket and you're good to go with either one of them. Although the Thunderbird does look a bit skinnier than Classic and might as well go along with your physique. I've personally seen guys looking like kids sitting on a Classic or a Bullet! Never felt the same when i saw people riding a Thunderbird though.

considering your weight i can say without thinking twice " It will not suite you ".. feel so sorry about that.. if you could spend money money for a thunderbird then go for duke 200. which will look better and also which is a better motorcycle. these Royal enfield bike use technology which is at least 50 years old. they just have the name. that's it. Go for Duke bro. That will look better and you will love it for sure.