Whilst I don't expect anyone to have an automatic respect for elders just because of their age, there is a place for common courtesy, after which point we earn extra respect from others according to how we treat them. I'm just 50, but I'm quite friendly with a lady in her late 60s who at first meeting is a bit of a dithery old lady. However, as I've got to know her, I find she has so much to offer aside from the things she can't do as well as I can and I'm beginning to value her opinion more and more.
I have also been called 'slow' in the past, although by people older or the same age as, rather than younger than me. I'm not as shallow as some and not quite so inclined to hang on to someone's every word just because they speak louder than everyone else. Nevertheless I've always felt the need to prove my intelligence and have thus gained a couple of degrees for myself.
Luckily I now find myself in a job where the team seem to appreciate the value of individual skills/experience contributing to the whole, but it's been a long time coming. Ironically, because of this environment, I now don't feel the need to prove myself so much. Thing is, I'm enjoying the OU study so much that I'm now just doing it for the sake of it. I've also developed a couple of hobbies for which I'm gaining equal respect.
Whether the fact of absorbing myself into my study and hobbies has caused me to stop dwelling on what people think of me, or whether it's just not happening anymore, I don't know. If they still call me slow or dozy, I can't say I notice it.
As an afterthought, I used to work with a very nice chap who was older than most of the team and quite deaf. He knew perfectly well that many of them thought he was stupid, but he told me once that he liked it that way. "When they think you can't hear them or are too stupid to understand them," he said, "it's amazing what you overhear."