I think the questions you asked (re: how they feel as teens, etc) has a lot more to do with relationship than anything else. Age may be a factor, it may not. They WILL get the "your mom is OLD" and you will get the "your grandchild ___" but that's not impossible to deal with. Going through teen years can be rocky regardless of what the "obstacle" is: age, religion, level of strictness, trying too hard to be cool, etc).
I am not an adult with older parents, but I did have my children at ages 31 and 34. My husband is 17 years older than me, so he is going to be 53 in December, with children ages 5 and 2. It does wear on him sometimes, but he's getting a lot stronger. We stay active, there's a lot of wrestling, playing catch, a little soccer, a lot of swimming, lots of walks down the beach, and now we're starting with the bike riding. We have to temper that with cuddling, reading, talking, etc when we don't have the energy to be the rodeo bull or run more laps....but that's not a bad thing. We actively seek out opportunities to bond, to have family time, to make our marks on their lives, to show them how much we love them. But because Jer is 48 years older than our oldest child, I do some things privately, because my realistic brain says it'll end too soon for their liking, no matter how good his health is, he'll still pass away when the boys are younger than many adults are when they lose a parent. I do little things to leave a legacy of who their dad is, since I think he's awesome, so the boys will know these things and have proof. I put photo boxes together of his "past life" (youth, travels, previous marriage, all that), I have a work scrap book that he doesn't even know about (ha) with all his awards and "stuff", we've done things like making a photo book we titled "The ABCs of Daddy" showing him doing things as a dad and husband (A-Z). On his end, he feels the stress of making sure that he can retire someday, but still have money for the boys to help with first cars, colleges, etc. The "normal" age to retire would be when the boys are 10 and 13! Yipes! We're on it though. :) Just something to think about. Grandparents are an issue. My fil passed away 3 years ago and my mil is 87 and has alzheimers. I was SOOO close to my grandma, so this makes me a little sad for my boys. I have a very good friend who the boys call Nana though and she kind of stepped into that "grandma role" though.
My dad is 63 and he adopted a baby when she was just a few hours old....she is now 8 years old. They're doing just fine so far. But my dad jogs 5 miles a day everyday, rain, sleet, snow, blistering heat, it doesn't matter. Only problem I see in their parent relationship is how he spoils her. They are doing fine. If he doesn't have the energy, time, or know-how to do the new cool thing, he at least has the money to put her in a class so she can do it. (Ballet, scouts, horse riding, softball, basketball, all of it)