I am 37 year old, all my life been eaten same things nothig unusual, a week a go I had a severe food allergy to nuts and pecans, I wonder why now?

It can happen. Food allergy can develop during adulthood. The most common foods that cause allergies to develop during adulthood include nuts and shellfish. I recommend that you carry an epi-pen and know how to use it in case you eat nuts by accident.
Epi Pen. Adult onset food allergic reactions may occur. As reported in an article by Joyce et al; 'The relative frequencies of reactions (systemic or localized) to specific tree nuts were reported as follows: walnut, 34%; cashew, 20%; almond, 15%; pecan, 9%; pistachio, 7%; and hazelnut, Brazil nut, macadamia nut, and hickory nut each were less than 5%.' I would suggest testing and avoiding all nuts.