Life expetency of a latex costume part is always hard to pin down.
I'd pretty much guess a well-maintained suit could last about 5-10 years. Keeping the suit in a controlled, cool environment would extend the life a little. Keeping the latex parts clean, inside and out is very important. Also a consideration is the brand of latev that is used. The best latex that I have ever used was a surgical grade latex. That stuff is tough and long-lasting.
But, in the long run, latex does eventually deteriorate no matter what you do. It's in it's nature to go back to nature.
You probably could, but I'm not sure why you would... It's terribly expensive compared to most of the available latexes out there... The cheapest Castin' Craft I found was $10.00 per/pint... That's $80.00 per/gallon. That's almost 3 times what I pay at Burman ($135.00 per/5 gal.= $27.00 per/gal). I can understand if it's all that's available to you, but I'd order mine elsewhere, and pay the shipping before paying $80.00 per/ gal.
If you are able to track down "Mold Builder" latex, that is good one to start with. I used that a lot in my early latex casting days. FX Warehouse sells a decent latex as well. Monsterroom(firstname.lastname@example.org)also sells some really good latex for a fair price. Monstermakers also sells latex online.
I had a DB P1 Mask, Bio, Hands, and feet a few years ago and I sold it all, because someone told me that Latex rots over time. So I figured I would dump it while the dumping was good, man am I sorry now. I think I got dumped on. Now here I am trying to start over.