I took my first Disney trip at 12 so I've always been interacting with characters as an older guest! The only disapproval I've ever encountered was a couple cranky guests but I think of it as them not truly understanding that Disney Magic is for everyone!
Some of the best ones from over the years... Merida was fantastic. My best friend got me a giant stuffed bear (like one of her little brothers) for my 18th birthday which I brought along with me to the parks on our next trip to take pictures with. Merida loved him and brought him to show to the animatronics of her brothers, who all retreated into their baskets and wouldn't come out until I agreed to hold the new bear!
I had fantastic interactions back when Rapunzel met with Flynn (seriously wishing they'd bring him back to WDW! He's my favourite Disney guy.), he gave me the smoulder and I got to see the crown that was in his satchel after they made sure I wasn't hanging out with ruffians or thugs and that I didn't smell like the colour brown.
Tiana and Naveen are also great, very enthusiastic about me being from the Land of Poutine, and asking ton of questions about how often we have poutine and where they serve it. They were so much fun every time we've gone!
And one of the best ones was when Mom and I met Tigger and Pooh in 2009 in the UK store. They horsed around with us for at least five minutes, taking tons of pictures, posing, and Tigger pulling me by the hand out the back door so we could dance to the band playing!
They pulled down these huge plush toys of themselves and were passing them to each other and between us, so we have these big plushes of Tigger and Pooh in our photos. They're hilarious, if I had them on this computer I would post because they are the greatest!
Chip and Dale love horsing around with guests too, they're my Mom's favourite so she always gets some time with them. I've never really had characters snub me because I'm an adult before: I think that, as many PPs said, that because adults are not likely to be afraid of them, they can carry on conversations with face characters that come as a breath of fresh air to their "friends"