I think an emailed picture would go a long way even if they have an age limit on paper. It is probably just a way for them to have a policy in writing when they want to turn some rust bucket away without someone taking personal offence.
And speaking of things in writing, if it is an age cut-off policy I would much prefer to have their pre-approval in writing than rather just talking to someone on the phone. The nice person who you spoke with on the phone may not be there when you roll in and no one wants either a needless confrontation nor to be turned away after a long drive. I'm sure pulling up the email would clear things up in a hurry.
At the risk of putting incorrect words in the mouth of a park owner/operator, I doubt there are many with 10 year age limits who would turn away 20 year old coaches that show great pride of ownership. And while there are MANY great folks with old RVs that do show their age, I sympathize with park operators who worry about the minority that may not be such great folks. Meaning, it may not be simply a case of being snooty as there may be some merit in the concept that if someone doesn't show their own rig respect, they may not be as inclined to show respect to the property of other guests.
Moreover, I suspect that some guests think they may be no safer than they would on skid row if a bunch of coaches in the park look like the equivalent of a skid row dwelling. Such a perception could hurt business. If you appreciate what I'm getting at.
Again, I might be completely off base, but these are my guesses why some parks have age limitations on guests' coaches.