In regards to whether or not you can start a character with a Master tag the short answer is, "Yes you can." But the long answer is no and I will explain why.
The fact of the matter is that this website is built mostly on OOC respect. When someone who has written a Master character comes up against another who has only just started (but has the Master tag because they started that way) then the newer person will be considered a much weaker character than the other. Of course it comes down to some roleplay and strategy in the fight but at the crux of it it comes down to respect.
As someone who has written a Master character (on and off) on this website for five (going on six years) I can tell you that I would consider my character to be stronger than yours and it would be reflected in our roleplay together. That being said I wouldn't powergame you (it is against the rules to do so) but I wouldn't hide the fact that I feel my character should win.
I recently had a fight with another character called Darth Animus whose character is far newer than mine (
). I did consider mine to be the stronger before the fight started and at the end of it we had a stalemate because Animus matched my writing and portrayed a strong character in our fight. The complexities of who is stronger is very nuanced and with many on this website it stems from OOC respect as I have said. My suggestion is build a character from scratch. It's more fun and you will avoid the problems I have explained in this post by creating a strong character from the bottom up.