You're not too old. Infantry does cause a lot of wear and tear, especially on the back and knees, so make sure that you're healthy enough to endure it. Sounds like you've hit a rut in your life and you're looking for a change, which is fine. It sounds like you're looking for your higher purpose in life and you know it's not your old job. But it's also probably not the infantry either. Just saying. Although you do get a certain sense of satisfaction from it that is hard to describe to civilians. Think hard about you really want, and why you want the infantry and CF. It's your life. You can do anything you want with it.