wondering if my brothers issues with ageing is connected to autism

Not quite, but I know of it a little bit, so take my answer with a grain of salt. My guess it has to do with his own fear of what he thinks comes with age, identity, responsibility.

I for one find it difficult to shift my taught nice-ways from childhood and growing up to act less so in these other surroundings where I came to exist later in life where people are simply not that nice when approaching, they've been taught something else. My nice ways even came off as flirtatious in the surrounding while it doesn't in other surroundings. I did not get what was going on, but have later understood I was young (but looked younger) and had dressed the part for the job I had (make up, clothes, shoes) like everyone else did. Before I was not that interested in my looks, but understood I needed to dress the part in order to get the job. I would study how the others looked but I did not study how they were acting, their attitude. (I would figure they had a bad day).  I was taught before that if you are well raised, if you are polite, nice, then that is the way to go everywhere, but now I understand it ain't. You got to crack the code where ever you are, adapt, in order to connect to others in that particular surrounding and in order to be part of the group. That can be very difficult and it can feel like the wrong thing to do, as if you are being untrue to yourself. Which then brings me to the conclusion that your brother wish to stay in the 18-year-group as he likes it more there (for what ever the reasons). 

Too what I think is common is that we (who have autism) is very mature in one way, but are immature (in lack of a better word) in another (but it can be a fun balance, can be exactly what everyone needs), but maybe he thinks that his immature/"childish" ways, if for instance, if he has a specific type of humor, is only appreciated in the 18-year old club, (with him mimicking like that) and it is seen as wrong in the 30-year old club he then rather stay in the 18-year old club. 

After now having left the not so nice/friendly surrounding for a while during the holidays I've watched others that works in the field I did back then and they are part of the group, they are the way I was, and it is not seen as they are flirting. So the way I was before was just right in that surrounding, "group", but misread, "wrong" in the other. Already I told my husband (who has been brought up in that other not so nice approach surrounding, only "home" he knows off) I do not think I will ever feel at home in this other not so nice approach world of his. I want to go back. however, would I remove my husband to my old world/surrounding he would feel out of place because to be truthful here he goes more undercover, is more one of them, in the not so nice approach world. Now, my old world still exist, and it is not age-dependent I think in quite the same way, but your brother may feel his is slipping through his fingers and it must be a terrible feeling. I feel as if this surrounding I live and work in will never be home to me. He's told me to be patient, but by now I know that I won't change my view on it. 

If he has a typical interest in something that is seen as immature in the 30-year old club he can still join a group where age don't matter or what  he could think is prescribed to that age 30-year old group. 

I apologize I write so much about myself/my own situation,, but other wise I do not know how I will explain how I've come to the conclusions I have about your brother. 

Not quite, but I know of it a little bit, so take my answer with a grain of salt. My guess it has to do with his own fear of what he thinks comes with age, identity, responsibility.

I for one find it difficult to shift my taught nice-ways from childhood and growing up to act less so in these other surroundings where I came to exist later in life where people are simply not that nice when approaching, they've been taught something else. My nice ways even came off as flirtatious in the surrounding while it doesn't in other surroundings. I did not get what was going on, but have later understood I was young (but looked younger) and had dressed the part for the job I had (make up, clothes, shoes) like everyone else did. Before I was not that interested in my looks, but understood I needed to dress the part in order to get the job. I would study how the others looked but I did not study how they were acting, their attitude. (I would figure they had a bad day).  I was taught before that if you are well raised, if you are polite, nice, then that is the way to go everywhere, but now I understand it ain't. You got to crack the code where ever you are, adapt, in order to connect to others in that particular surrounding and in order to be part of the group. That can be very difficult and it can feel like the wrong thing to do, as if you are being untrue to yourself. Which then brings me to the conclusion that your brother wish to stay in the 18-year-group as he likes it more there (for what ever the reasons). 

Too what I think is common is that we (who have autism) is very mature in one way, but are immature (in lack of a better word) in another (but it can be a fun balance, can be exactly what everyone needs), but maybe he thinks that his immature/"childish" ways, if for instance, if he has a specific type of humor, is only appreciated in the 18-year old club, (with him mimicking like that) and it is seen as wrong in the 30-year old club he then rather stay in the 18-year old club. 

After now having left the not so nice/friendly surrounding for a while during the holidays I've watched others that works in the field I did back then and they are part of the group, they are the way I was, and it is not seen as they are flirting. So the way I was before was just right in that surrounding, "group", but misread, "wrong" in the other. Already I told my husband (who has been brought up in that other not so nice approach surrounding, only "home" he knows off) I do not think I will ever feel at home in this other not so nice approach world of his. I want to go back. however, would I remove my husband to my old world/surrounding he would feel out of place because to be truthful here he goes more undercover, is more one of them, in the not so nice approach world. Now, my old world still exist, and it is not age-dependent I think in quite the same way, but your brother may feel his is slipping through his fingers and it must be a terrible feeling. I feel as if this surrounding I live and work in will never be home to me. He's told me to be patient, but by now I know that I won't change my view on it. 

If he has a typical interest in something that is seen as immature in the 30-year old club he can still join a group where age don't matter or what  he could think is prescribed to that age 30-year old group. 

I apologize I write so much about myself/my own situation,, but other wise I do not know how I will explain how I've come to the conclusions I have about your brother.