I'm 33yo 6'4" 195lbs and skinny my problem is if i do 20 pushups i can barely do them then after i'm shaking and completely exhausted?

Start slow: your program seems a bit too vigorous for you. Try 15 minutes of walking three times a week. Then perhaps two days a week some push-ups and situps perhaps no more than 10 per set and no more than 3 sets at a time with a minute or two of rest in between each set. Try this for two weeks. If this work out becomes easy for you, then increase the amount of time walking/sit ups/push ups by 10% each 2wks