I am 49 years old and I work as freelance consultant on e-commerce projets. Honestly, it is impossible for me to work (which means mostly sitting) for 3-4 hours in the morning and 4-5 hours in the afternoon and also sit during lunch. If I do that I will either fall asleep or be unproductive for most of the afternoon. At lunch I spend at least one hour walking, running or biking. At the least I must get outside, whatever the weather.