Question about starting C25k

Hi everyone,
I just downloaded a C25k app for my android phone and was planning to start tonight. I've been increasing my walking speed and distance over the last week and did some test jogging Monday and Tuesday nights. Yesterday I walked with a couple co-workers at lunch. One of them walks really fast. REALLY fast--like I might be able to keep up with her pace if I broke into a jog fast. So I walked faster than was comfortable for me for almost 2 miles yesterday at lunch. Today my quads are sore (probably from taking three times as many trips down the 5 flights of stairs to the work lobby than usual) and my right shin is bothering me when I walk (probably from speed walking with the co-worker yesterday). 
Would it be better to hold off on starting C25****il the shin stops bothering me, or should I just go for it?
I'm 46yo, have been dx'd with chondromalacia and patellar arthritis in both knees (although I've had lateral release surgery and arthritis clean-up on both knees and have been pain-free for about a year, I've lost about 50 lbs since January and have been feeling great with the extra walking and little bit of jogging.)
Thoughts please? Thank you! Meri

FWIW, I started tonight anyway. Did my 8 sets of 1-minute runs, then cooled down and had a ways to go to get home, so I did two more 1-minute sets. Feeling pretty good.

According to my Fitbit (walked around the house a bit before remembering to turn off the stopwatch on the Fitbit so there's about 5 minutes of puttering included):

Activity record from 08:05pm to 09:11pm

Duration 1hr 6min
Cals burned 477
Steps 7329
Floors 13
Distance 3.37 mi
Pace 19:33/mi

Could there possibly be a runner in this body????

 One thing - always listen to your body and don't push too hard if you're in pain. Soreness is a different issue, but only you know your body and your limits. 

Great job on the start. If someone would have told me 2 years ago when I was weighing 400+ lbs that I'd be a runner, I would have laughed. There's no way of knowing what we are capable of unless we try and push ourselves :)

The BEST thing you can do is listen to your body.  I am typically sore from exercise every single day in some part of my body. More exercise usually helps me feel better.  However, when I have certain joint pain, I KNOW when I need to modify and slow down a bit. 

On the subject of powerwalking:  I do this sometimes with my hubby.  It is actually harder for me than jogging.  My joints take a greater beating from PW than jogging. 

I never thought I'd be a runner until I started-and I love it and have been doing it faithfully for 3 years now.  You may just end up loving it too!

A few words of advice:  Only do it if you like it, and get fitted for good running shoes.  Go to a running shoe store, not a big box store.  For approx $100 you can get fitted for the type of shoe for the way you run...it is worth it.  The first year I ran in shoes I bought at a sporting goods store....I lost toenails on both feet due to poor fit.

Have fun!

Thank you Alison and Kim. I felt great for the first week...a little more stiff after W1 day 3 and was a bit anxious about starting Week 2. But I did W2 Day 1 and felt pretty good for a while, but then the knees started protesting. They ached later that evening and all of yesterday. I did not have time to ice them but plan to get my knee ice packs in the freezer after work and will ice tonight to get the mild swelling down.

Much as I think I'd like to keep running, I think I have to stop. Spent most of last year not able to walk without limping on one knee or the other and I don't want to go back to that.

Kim, I have been going to a running store for my shoes since 1996 and love the place and the great fit I get. Just bought new shoes this past weekend, in fact. My problem is supination so it's really important that I get a nice neutral shoe. Especially for my poor knees.

Next up: trying out my son's bike and then possibly looking for a decent used bike for myself. At least until the cold weather closes in and makes it too cold or dangerous to ride. Then I switch back to the gym.