1. Ash and co don't age. The reason: nobody wants to see eps of Pokemon in five years or so when Ash is an adult trainer. Also, this can happen in cartoons. In the Simpsons, for example, I've heard them say what year it is many times, and most of the time it's a different year, but they still don't age.
2. Ash is 10. May is 10. They are too friendly and too alike for there to be four or five years between them.
3. Delia cannot be in her mid-twenties. First thing - what proof is there? She could be in her mid-thirties! Also, are you saying that she wasn't even an adult when she had Ash? Lastly, she's friends with Oak, and seems to know him well, too well to only be in her mid-twenties.
5. It would be illegal for Brock to travel with Ash, May and Max if he were 18 or over. Why? He isn't their legal guardian. And, does he look 18 to you?