There are two guys wearing these at the moment. Guys who never stopped and new guys trying them out. It is a great look and a must if you have a suit rotation over 5 suits. Of course if this is all you want to =wear then you can buy from the word go. Up to you but would recommend shopping a bit higher up the high shop chains should you wish to buy off the peg.
The reason being is that single breasted jackets are much more done and if the high streets are trying a pattern out to get a small portion of a market then you may expect some kinks and mistakes along the way. So going to a more respected suit shop will pay dividends.
So places I would do a double breasted first time to gain confidence:
Sporting event: Wimbledon, Horse racing, Lords Cricket ground
Going out: The Theatre, Opera (if not DJ compulsory)
Friday work day
Summer weddings in more formal locations
Double breasted casual jackets are great in tweed but also rare. Are done more in coat styles but do add a great look. These can be worn to clubs and bars around the city and should be paired with contrast trousers in cotton or cords for a playful visual punch of colour.
Also double breasted suits are to be worn on the fitted side rather than the loose appendages of the late 20th century which hung off the body in the most inelegant of ways.
Trim and wide peak lapels (3 3/4" - 4 1/2") are the fashion but a classic style will stay looking good for longer so a medium peak lapel is best (3" - 3 1/2").
Below is a great gent wearing a wide 4" peak lapel and looks very elegant but with a fashion statement about it. Great look for that very individual suit to play around with.