As a child, I definitely felt lonely. When you're stuck at school with people for 6+ hours a day and interactions are non-existent or negative, then that's very hard. I think younger people care a lot about fitting in.
The older I get, the less I care (though I do have my husband around now, so I'm never completely lonely and perhaps that's the key). I think, perhaps, as a younger person I might have wanted friends for the sake of wanting friends - because people were supposed to have friends, and not because I actually enjoyed any of the things that people like doing. At university I definitely tried to connect with people, even went to night clubs when I'd rather have been at home, relaxing, but it just wasn't me and was always very forced.
Now, I know myself well enough to know that it isn't worth forcing these things when I'm not getting anything out of it. I'm never going to be a social creature, it isn't what I want, and I'm much happier keeping myself (mostly) to myself. I think that, did I not have a family that I adore and love being around, I could very comfortably live my entire life in my own little world.
What doesn't work at my current stage of life is that I have a young child whose social life depends on mine. She has led me to one or two genuine friends (my first ever friends) which is lovely, but I have also pushed myself into a world of socialisation that just isn't right for me - the cliques and bullying, nights out, big group conversations, competitive behaviours and jealousy. It's hard going and I'd rather not be doing that, but a little person depends on me for chances to interact with others her age.
I believe (and hope) that at least when I'm ageing I should not have as many troubles with loneliness as NTs. I will be perfectly content to retreat into my own little world as I get older.