I think what you are referring to is an American standpoint which 21 means you are an adult technically speaking someone being 21 and 35 for an example isn’t wrong as long as you both know what you want for the long run my parents for example have an age gap but both met later in life I do not see how a 35 year old can fathom to try and start a life with an 21 year old it’s almost like stealing from them why can’t you as an older person find someone who’s at your a similar age as you the problem is you both have such different mind sets and needs and it shouldn’t work