Start training today! Should be awesome. You'll be amazed by how quickly you gain fitness in walking. I would start by walking out from home for 10 minutes and then walking back. Doesn't matter how far you go, doesn't matter how fast you go. Just walk out for 10 and then walk back.
Increase your pace gradually as well as the time you walk. Push yourself a little bit, but not too much. Walk with your friend when you can - get out and enjoy!
Lose 25lbs by 15 April (10 Mar)
Get to 100 kg (220) by 1 May (7 Apr)
Be 205 by race day - 14 July
One-derland by 1 Sept