Seniority trumps all previous experience. There are certain checks you can skip if you have previous command experience however the actual promotion is only given when your number is called. 30 is not too old so you would still manage to fill your pension and have several years on the maximum salary.
About FR the grass is always greener on the other side, I was recently speaking to people who currently work there and people who have recently left. It seems like there is a misconception that it is an easier life elsewhere, that is not entirely correct. A days work in EI can be just as hard if not harder than in FR due to the earlier starts and later finish times when you compare the two. The real difference is annual leave if you manage to get primary summer months. The only downside to the summer leave is that the season is from April to October so peak summer leave is not guaranteed, but at least there is a chance!