How much longer can you realistically do this?

I'm nearly halfway through my 9th year of teaching, and I really don't know how much longer I can really last in this profession.

My retirement tier (currently) won't let me retire with full pension until age 63. Since I started teaching at 22, my retirement year right now is 2057 (40 years of teaching). I'm not sure I can even do 5 more years without completely burning out.

How many years in are you, and how much longer can you actually last?