I'm 33yr old woman, married and childfree. This is my suggestion regarding loneliness, only as it pertains to friendships (specifically female friendships) in my experience. I have a very close group of girlfriends that I have cultivated since highschool. Its a couple of my HS friends, a couple of my college friends, and a few post college friends. I am the person who brought the group together, but we are all quite close now. The last of the group (excepting me) just had her first kid. they all have kids, from 1-3 each, under 8. To be frank, it sucks. I love them all dearly, but at this point, it is really difficult to have a close friendship with any of them, as they are all so deeply entwined in the baby/kid phase. When we all get together, either they want to bring the kids (in which case it just turns into watching them all wrangle and referee the kids), or they spend the entire time talking about potty training and scabby nipples. Charmed I'm sure. I try to remind myself that this wont last forever, but it still sucks sitting around a table with 6 smart, funny, interesting women, and having the conversation continuously turn to that crap. Like, can we discuss ANYTHING else?! A good book, a new movie, an amazing new album, ANYTHING besides kids! I do my best to be a good and supportive friend, b/c they do the same in their way, and remind myself that in a handful of years things should (fingers crossed!) return to some semblance of normality. I dont mind kids, I just dont want any of my own, and they are all respectful of that choice, just as I am of theirs. Being a good friend is a two-way street, and I wouldnt waste my time on relationships that didnt feel reciprocal.
That being said, in the past 3-5 years both my husband and I have been making a concerted effort to find and cultivate friendships with other childfree people for this reason. We enjoy traveling, live music, craft beer, good wine, and just generally having a good time after 7pm (when our other friends needs to get home to get kids to bed...), so we have been really trying to find others who share our interests and whose company we enjoy. While the vast majority of our friends who do have kids have managed to find a good balance between parent and still the awesome person I used to be, there will always be some amount of disconnect there.
Dont fall victim to the classic bingo line of "but wont you be lonely when you grow old?" from others. If you know kids arent for you, live the life you want with no regrets. But I would recommend that you try to fill your life with like-minded, or at the very least supportive and understanding people whose company you truly enjoy. Cultivate relationships with friends who love and support you, whether or not they have kids, but know that those who do will likely have a time in their lives when their priorities will differ from yours, and thats ok! But that is why its nice to have a good group of friends on both sides of the kid fence!