As mentioned in an earlier post-I saw him in concert in Sept 2011, his voice was about the same as is shown in this video. Has had some health issues in the past decade and is also celebrating another birthday in November.
Since leaving Chicago in 1985, he has performed a very limited number of concerts each year-so that has saved his voice. He also appears to take good care of himself. In his late 60's now, his voice still soars.
PBS special from 2001