For age - wide paths/ steps/ entrance door to house. Chose material carefully - nothing that gets slippy when wet.
A space between the front door and the hallway for boots, umbrellas, coats etc. The old Victorians had small glass porches - bring 'em back! If need be move the front door further into the hallway.
Widen ALL the doors, especially downstairs.
Downstairs toilet.
Drawers in the kitchen. We have only one cupboard. It is floor to ceiling, 6ft wide and has jib doors that sit flat to the wall when open. Everything goes into it, doors close and the kitchen is tidy!
A fireplace. It is so nice for my mum to sit by the fire as walking is difficult. It brings cheer and comfort to her.
Laundry upstairs - best thing I ever did. The machines are on the landing at the top of the stairs in a cupboard. Two jib doors that sit flush to the wall when open (sse a theme here?) but you don't notice it when closed. Bloody MARVELOUS. No more carting laundry up and down stairs.
An upstairs toilet that is not in a/the bathroom. That is a very nice separation that enhances my life. DH is smelly!
Really good insulation.
Pay attention to windows - cold in winter but airflow in the summer.
Underfloor heating.
Really good lighting.