You chose to have children. Some people know very well why they are choosing not to. Some don't and blithely bypass the whole thing. Those who have yet to will find out - are you really envious that they are enjoying their pre-baby time more than you did?
If they are directing judgement at you about your parenting then you have every right to be annoyed and say so. Otherwise smile and laugh inwardly. Why would you let them get to you, unless you have a niggling doubt in your certainty that, unlike you, they cannot achieve what they aspire to?
I'm expecting our first and know something about what to expect but am also very aware that there is a lot I cannot know until it happens and I experience it for myself. I am also aware that, though there are significant basics in common, every person's experience is different, as parents and babies are different. I see huge differences between friends' parenting styles and the ease or difficulty their babies allow them.
The friends I will turn to for advice, and happily discuss parenthood with now, are the ones who tell me about their own experience openly, highs, lows and surprises, while being able to distinguish between what is universal and what is their subjective experience.
Their advice is useful for exactly this reason, it is couched in terms of 'this is what works for me' not 'I am the universal guru just because I've done this thing and you haven't'. That attitude is not uncommon though, along with the uber-smug assumption of parental elevation; 'you can't possibly know anything about life until you are a parent'. Some of us have been putting up with that sanctimonious crap for years, often from people who have limited life experience or fulfillment in other ways (perhaps the most naive pre-parents are the most likely to continue through life in this self-absorbed, self-justifying way?).
I am making the most of my remaining pre-baby time precisely because I know I am going to lose a huge amount of freedom, time, sleep and ability to concentrate once it's here. I don't go round making naive coments to parents but I don't need any parents making smug comments predicated on my presumed naivety either.