The quote is also absent from Google Books pre-1960 and from JSTOR. I imagine this follows the normal pattern of a clever quote being dreamed up by nobody in particular and then added to the Twain canon because it sounds like something he would have said. 

Terry

Terry Ballard
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-----Original Message-----
From: Mark Twain Forum [mailto:[log in to unmask]] On Behalf Of Click, Benjamin A
Sent: Monday, February 14, 2011 10:49 AM
To: [log in to unmask]
Subject: Re: Mind over Matter

Always thought that was baseball great, Satchel Paige.


On 2/13/11 6:46 PM, "[log in to unmask]" <[log in to unmask]> wrote:

> I have often read this quote as being by Mark  Twain.
> =20
> I'm convinced, however, that's not the case.  Barb Schmidt would  have
> included it on _www.twainquotes_ (http://www.twainquotes) .   And it's no=
t
> there.  Or if it's there, I'm blind
> and haven't seen it.
> =20
> Should anyone have any convincing evidence otherwise, I'm pretty
> sure it will surface here on the List.
> =20
> Best,
> =20
> Roger Durrett
> Charlotte, NC
> In a message dated 2/13/2011 4:46:45 P.M. Eastern Standard Time,
> [log in to unmask] writes:
> =20
> I have  seen this attributed to Mark Twain:  "Age is an issue of mind ove=
r
> matter. If you don't mind, it doesn't matter."  My questions are:   Did M=
T
> originate this quote?  Or, at the very
> least, did he at some  time say or write it?  If not, is the source known=
?
> =20