If men are honest, many men with wives over 30 fantasize about their wives as they were much earlier in their marriage.

Of those who got married to their current wife late in life, many probably fantasize about a young women they once bedded, an imaginary women, or, hopefully, their current wife as she looks in old family photos.

I see very little difference in fantasizing about a young boy and fantasizing about a woman other than your wife.

Here's another option:

Cuddle with her and try to pleasure her and don't worry about your own orgasm.

Later, when you are alone, masturbate so that you won't be tempted as much by real boys.

If she's not terribly interested in sex, another alternative might be drugs that lower libido to a manageable level. Some anti-depressants have this as a side effect, so if you are depressed this could kill two birds with one stone.

Oh, one final thought:
Every minute of the day you spend praying, reading the Bible, or meditating is one minute you are not distracted by sexual thoughts.