It is a stupid reason to bail out of your aspirations because you can lose so many life long opportunities and benefits by ensuring you fail before you have even started (self sabotage)
It is not a stupid reason to feel as you do. Clearly you feel very self conscious about how your physical self has changed? Has your emotional self changed in the same way? - No probably not. That is the irony of life, and the effect of life's hard knocks which etch onto our faces. We are as we are. But at the same time you have changed in physique so have all of your friends and work colleagues. Some people have iron discipline to keep a workout, keep walking, keep exercising; others who are wall to wall looking after kids, dogs, partners, work struggle to add working out to that list. Life gets crazy busy at times with not enough time to breathe and then something has to give.
But some of the most caring, funny people are the heavy guys. Thank goodness, someone else has put on more weight than me! Thank goodness others have major flaws and do not wear well. That is the funny part of life, watching how people we know well sag and wear out. Good - because no matter what we measure ourselves on a continuum scale and make comparisons between those people we know. It can make us feel better, it can make us feel worse. We are probably not the worst or the best but we wear our true self from within. Spend your year stressing over how you have changed when you could have gained so much more looking outwards and just accepting you are how you are. Your physical self is just that, a means to an end and life is short and temporary. You can never relive that last minute. So treasure your physical self. Feed it with fruit & veg and avoid the processed foods. Drink lots of water. Then max out your life's ambitions, forget how you think you appear and aim for the stars.