I'd take him at his word. He sounds like a good guy who's got really strong boundaries. He knows how he expects to be treated and is able to not accept anything less. Basically, he sounds like he's got his shit together.
That being said, I doubt that you can suddenly "decide" to trust someone. Thing is, your lack of trust is not because of what he's doing (unless there's something dodgy which you haven't told us) it's because of what's going on for you. You need to look at yourself and your past if you're to move forward.
Part of what you'll need to do is look at the past and figure out what you can learn from it. For example, were there warning signs that you didn't heed? If so, how could you use the knowledge you have to make better choices in the future?
I think that letting go and being able to trust also hinges on personal resilience. The knowledge that even if it all goes pear-shaped and you didn't see it coming, that you are strong and (after a time of grief) you will get through it and come out stronger.
A bit of counselling wouldn't go astray if you need support in this.
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Oh, and Jester is right. Age has nothing to do with honesty. There are honest 18yos and lying 60yos It's about integrity, not age.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.