mutton dressed as a lamb
rob the cradle
(be) over the hill
to be knee-high to a grasshopper
to act your age
feel your age
(live to a) ripe old age
silver surfer
get on in years
long in the tooth
An elderly person who uses the internet
To live until you are very old.
a person who tries to look younger by wearing clothes designed for younger people
Realize that you are no longer young
no to behave as someone younger
Have a romantic relationship with someone who is much younger than yourself.
Very young or small child
Too old to do something
Someone who is growing old.
Reach an age when you can no longer perform as well as before.