I'm with the others about not cutting your calories too much. Especially being young your metabolism is at it's peak and cutting down too severely can actually damage it.
I would recommend around 1400 to 1500 calories a day.
Walking miles a day is probably one of the slowest ways to lose weight. Have you heard of HIT? (High intensity intervals). What it I told you instead of spending hours walking, you could do 2 to 3 strength training sessions a week and two 20 to 30 minute sessions of cardio, and you'd likely burn many more calories and have more definition quicker? It's much more efficient to lose weight. However, when you lose fat this way, the scale number may not change but you can easily drop a couple sizes and actually look much better.
It was hard for me to change this perception because my scale hasn't budged for weeks. But I decided to dive in anyway, and while the scale hasn't moved, everyone at work keeps exclaiming how much weight i've lost in the last month. They can't believe the scale didn't budge. If you're willing to give it a shot, and save a lot of time and gain efficiency here's what I'm doing:
Diet: *MOST IMPORTANT PART
if you eat 1200 calories of crap, it will not help you, as more research is being done, a calorie is no longer a equal calorie. There is a huge difference between 1200 calories of chicken/fish/veggies/hummus/nuts and three lean cuisines in a day. I did this in the past, yeah I lost weight, but I had no tone, and was "skinny fat."
This is what I do/recommend
High protein, moderate carb, moderate fat diet.
Lots: vegetables/tuna fish/eggs/chicken/turkey, mustard, hot sauce/salsa
There is some: nuts/protein bars/bacon, mayo, tomato sauce, alfredo
There is no cookies/bread/pasta; No sodas or diet.
Exercise:
two cardio sessions a week, you can do more if you have time, but try to keep them separate from your weight training. Do something you like. I like spinning, everyone's different.
2 minutes of warm up
Then for 20 minutes: 30 seconds of all out as fast as you can, followed by 30 seconds of slow/moderate pace of whatever cardio exercise you pick
then 2 minute cool down.
HIT has been shown to be much more effective for fat loss than a long walk.
2-3 days of weight training.
3 sets with 8 to 12 reps
Squats
Lunges
Chest Press
Push ups
Pull Ups (modified if needed, I need tons of modification still!)
Bent Over Rows
Starting out, it's more about learning proper technique. Add weight later, you will not bulk up, you will get lean.