My son told me today "Daddy, you don't look any different than you did when you were 35." Of course, since my birthday was yesterday, I would hope not.
But, if you were to compare now with, say, my engagement pictures, you'd see several differences--shorter (and whiter) hair, the beard, a few wrinkles, and a few extra pounds, just to name a few.
I think our spiritual life is like that, too. It's hard to measure sanctification on a day-by-day basis; it's only when we look back over time that we can see God working in us to make us more like Him.
Now if I were to look exactly the same as I did 12 years ago (assuming that I'm not Dick Clark), something would be wrong. In the same way, if my life spiritually looks the same as it did back then, I think you would be hard pressed to say that any growth took place. And in fact, I would argue that if no growth is evident, you ought to question whether there was ever a birth.
So as this body slowly deteriorates, I'm reminded of the change that is happening on the inside, and I praise God for that.
Therefore we do not lose heart. Though outwardly we are wasting away, yet inwardly we are being renewed day by day. (2 Cor 4:16, NIV)