Will job change in admission season hurt my profile ?

All good questions and I empathize with your plight. It's not any fun to grind out a daily work routine in a place where you are unhappy. It doesn't sound like your job change would necessarily be an upward move, which could create some challenges as it pertains to your application. Generally, any moves you make in your career should be onward and upward--sometimes even a pay increase can be a valid and "excusable" reason for a move even if it's just a lateral one. If you can weave a good story around why you left that does not center on your being unhappy at your old job, it's a better play. If you can somehow justify that it is a move which better challenged you or provided you with some kind of necessary experience you felt you lacked in your old job, that's good too. If you can't do either or both of these, it may be best to just tough it out, make the best of it and try to leverage your leadership opportunities and potential recomendations from a "seasoned" job. Another option is to make the move and then delay b-school applications another year or two. I wouldn't stress about your being an "older" candidate. I was over 30 when I went back (to a top 5 school), and sometimes being older can even help you differentiate yourself, so long as you did something interesting and progressively responsible with your time. Better to come in with a couple of years in a new job that you love and are more posititve and passionate about than to go back now just because you are under 30. Being under 30 does not really get you anywhere with an adcom.