He is as old as Scholes in 2005. Scholes gave us a few world class seasons since then. I am not sure that the injuries of last year will be the norm. Again for comparison Schweini played 28 matches last season. Scholes played 27 in 2005-2006.
If he is past peak then it is bad, but if not then we will have a fantastic midfielder for a few years. At the worst case, I think that he'll be a very useful player and a much needed leader in a team who lacks them.
Anyway, I am most excited for this signing because there is the possibility that Van Gaal will Schweinsteiger Schweinsteiger. How cool that would be?!