For years I knew most of my major scales, (had never really thought about the minors too hard) but not all of them - I avoided the trickier keys like F#, C# and B. I finally made a pact with myself that I wanted to know them, inside and out, so they became part of my practice routine. Once my majors were solid, I set about getting my natural minor scales under my fingers, using what I know about relative major and minor scales. All in all it didn't take very long before I was playing through all of them, mistake free, as part of my regular practice, and I really kick myself that I didn't knuckle down and do it years ago. Old dogs CAN learn new tricks, and usually it's a simple matter of self-discipline. So, to the OP, do what Rowuk says, be like Nike and just DO IT. It might be frustrating at first, but you'll be playing them up and down and inside and out before you know it, and it will make you a better player because of it.