Using Old Paint on Inside Wall
Unless your paint is pre-1985, you really don't have to worry about lead.  

Paint doesn't expire but it can go bad.  

It's totally OK to use your high-VOC paint.  You're just not allowed to sell it at retail, or sneak it in to bypass local environmental regs.  Trying to educate 70 million people in the 12-state areas is a lost cause, so the (US and state) government's approach is to ensure that any product you buy in a local store is legal. As far as products you already bought, they're not worried about it. 

So if this is "new old stock" sitting on your shelf, for God's sake, paint it before it goes bad.  The second best way to dispose of old paint is to paint something you don't want, then throw that thing away.  The worst possible way is throw it in a landfill, it'll leach chemicals for years.   Let paint do its job.  It's designed for that. 

That said... 

One curse of low-VOC paint is it's vulnerable to mold and mildew, in the can.  If you open a can of normally mild-smelling latex paint, and it's Stinky, that's what has gone wrong.  Do not paint stinky latex paint on anything (except for the "paint something you don't want and throw it away" rule).  Believe me, you'll want to throw it away!

I have no idea how toxic it is, except for what it is - mold and mildew, which, yes, is not good for humans to be around.

There are lot of answers for how to encapsulate it, but none of the answers have reported particularly good results in the long term. Having forcibly removed much worse paint, I'd remove it.  Latex is pretty flimsy stuff, and it'll practically fall off the wall with enough persuasion, i.e. wetting and firm nylon brushes.  The goal being not to damage the substrate so you don't have to drywall rework.