Starting off

monosharp

16.5 stone, male. I've being more or less on and off training for a few months so you could say i'm really only starting seriously now the last week.

Managing 4km run in 25 minutes, 15 sit ups < 1 min, 10 push ups < 1 min.

I don't think the running is too bad but i think i'm way way below what i should be in the push ups/sit ups department, even for someone starting off.

Can anyone give me a bit of advice on where to go from here and what i should be doing situp/push up and running wise and any other exercises i should be doing ?

Boru.

Post all your current details height, weight, age, bodyfat % if you know it, training goals, time available to train, motivation levels, preffered method of attaining that goal,

Diet - what times you eat, what you eat, quanities, how often, any particular diet type, e.g. vegitarian, low carb etc. Give us as much detail as posisble and we will do like wise

rubadub

Doing push-ups and sit-ups (I would prefer crunches) should not be a in a rush (I see you are timing them for some reason), it is harder to do them slowly with correct form, you do not have momentum helping you. 10 push-ups at 16.5stone is not bad IMO, since you are lifting a fairly large weight. i.e. when I was 90kg I could only do 1 chinup, now at 75kg I could do about 13, but strap 10kg onto my back so I am 85kg and I could only do 6.
You should only be doing situps and pushups every other day, otherwise you risk overtraining.

If you are trying to lose fat I would highly recommend doing proper weight training, with heavy weights.