Similar story to yourself i guess.Always struggled with my weight, really started gaining weight at around age 8/9 Hit 19st by GCSE and 21st by A levels. Lost a shed load around 10 years ago and got from 23 and half to 16 through sweat and more sweat.
Injury and what i call the big loser mind set ( i've lost it before its ok if i put on a stone or 2 because i can get that off in a few months etc)
7 weeks after my 30th birthday I walked into a slimming world meeting and weighed in at 23st 7lb. That was Feb 2012. I'm now tracking at around 18-19st depending on injury. (Had a few ankle problems this year)
If you can get to one and you can suck up the courage to walk into one (yes you maybe the only guy there) I highly recommend getting to a SW group. Never done WW so can't comment but i'm sure its equally as good.
Also the key to getting it off and keeping it off is exercise, I started at over 21st and did the couch to 5k running program. my first session i lasted 58 seconds at 8kph before i had to stop. This year i have completed 3 full 10k races in 1 week (May) 3x 10km laps in one day at a 24hr off road event in July, and on 1st September I did a half marathon without walking in 2hr 27m and 59s.
Without the exercise I would not have kept the weight off. Find something you enjoy, boxing/martial arts/cycling/swimming/rugby/football/ racquet sports anything that gets you off your arse 2-3 times a week for 45mins to an hour.
2 things you could try is. http://www.parkrun.org.uk/events/events/
this is a friendly non competitive 5k event run every week in parks across the world, there are no medals no 'winners' and you will see everything from super whippet type 16/17 min runners right the way to the walkers who cover it in 50m+
I started in the Coventry one and quickly got addicted to bettering my time. running just a few meters more than last week, the next tree etc. From there I got involved with a local club and never looked back.
Second thing if you don't fancy being seen hot and sweaty in the park check out. http://www.ddpyoga.com/
Years ago probably before your time there was a wrestler in the WCW called diamond dallas page. Well this is what he does now. hence DDP. After injury he did yoga to rehab and then formed his own workout program. Please watch. http://www.youtube.com/watch?v=mQdJgM2o9GA
this guy is Called Arthur Boorman, also this one is more of his story http://www.youtube.com/watch?v=qX9FSZJu448
Youtube is full of vids from DDP yoga so check it out.
Warning though the program is not cheap! it cost me like £70 for 2 dvds but they are well worth it providing you use them. options to pay over 3 monthly installments etc. also xmas soon might be worth dropping hints.
If you can get on this alone do it! if you need help join a club. Remember losing weight is not miserable, exercise is not punishment for being fat. Find fun in what you do and you will go far.