When I wrote CAPTURE THE SAINT, an obvious "problem" was
Simon Templar's chronological age. He would, in truth, be over
80-years-old. This was a problem that Leslie Charteris also
encountered, and we both found our ways of dealing with it. 
In Charteris' THE SAINT IN PURSUIT, Templar deals with a situation resultant from WWII. He actually mentions how much time had passed since then (about 25 years), and anyone with rudementary math skills can figure out that The Saint must be about 60. However, his age is not mentioned directly, and his behaviour is that of a younger man.
In Charteris' VENDETTA FOR THE SAINT, (mid 1960's) , there is a scene
where the Saint thinks to himself that if he were younger he would jump
the two thugs beneath him, but instead he sneaks away. Yes, if we want
to figure it out, he is too old to be our dashing hero -- but we let it
go. In my CAPTURE THE SAINT (1998), I pushed it even harder. It is a
present day sequel to THE SAINT IN NEW YORK, published in 1935.
Charteris said the story takes place in 1933. The Saint, in 1933, is 31
years old. CAPTURE takes place in 1990;s. In real life, the Saint would
be over NINETY years old. Well, he isn't. His first line of dialog in
the novel sets it up: "Mythological characters such as myself seldom
age at the going rate."
Little Viola, the kidnapped child from SAINT IN NEW YORK is now an adult enlisting the Saint's help. Here is how I handled it:
"You are not six years old anymore, and I am certainly not thirty-one. You are a grown woman, and I'm..."
"....The Saint," asserted Viola, reciting a memorized newspaper
account, "an astonishing combination of heroism and terrorism, the most
mysterious figure..."
"Spare me," Simon laughed, "I was always easy copy for adjective-addicted reporters."
And that's that. He may be in his 90's in the "real world," but
in the world of series adventures, he is always "hero age."