ONE thing NOT to do is to make it caricaturish!!  If you TRY to make it cliche' it's going to look it.  I saw a production of Moon Over Buffalo and Charlotte's MOTHER, played by a much younger actress, shuffled and was bent over like a 100 year old lady and it looked ridiculous.  Just be careful.  Look around. OBSERVE people who ARE that old and see how THEY move.  I think you'll find that many 75 year olds that are spry and energetic, don't move all that much differently than normal healthy younger people.  They don't move QUITE as fast and with a slight bit more caution, but I know people older than that who move better than I do.  There's one guy I know - an older friend who is likely now about 90 (reason I know is because I went to his 80th birthday party quite a number of years ago - 10 maybe more) but he moves better than I do.  He runs at the gym and so forth.  I can't run to the mail box but what I'm out of wind.  And he's in great shape.  Likely to live to 100 no doubt about it.  So look around.  See those who are 75 or thereabout, and without doing a cliched act of them, try to duplicate how they move.  If you overdo it - it will show and look ridiculous.  Go for realistic and legitimate if that's what you need to do for the character.

TonyDi