Whilst it is always advisable to take a professional approach to independent publishing to produce a quality book people will want to read (hire an editor, cover designer, proofreader etc.) the bottom line is that there are no limitations on how and when you can choose to make the final leap.
JK Rowling was 'proud...that when I "unmasked" myself to my editor David Shelley...one of the first things he said was "I never would have thought a woman wrote that."'... Nichi Hodgson... went so far as to question whether Rowling had 'betrayed women'.
Scottish writers are particularly successful in the crime genre. Something approaching a third of all traditionally published fiction in the UK this year falls into the category and it's one where Scots punch above their weight.