Honestly, I got pregnant with my oldest at 19, had him when I was 20. I am now 26. I did get a lot of awkward treatment at the time, I suppose. Maybe even for the first couple of years. But now, even though I too look rather young for my age (or so I'm told, I can only assume it must be true considering how often I hear about it lol), no I do not still feel like the stigma follows me around.
To tell you the truth, I think it is more about how you feel about yourself, and how mature you actually are and how confident you are of your adulthood. If you live a certain kind of life, or you feel like you should be treated like a child, people are more likely to treat you that way, or even if they aren't, you are more likely to feel like they are. If that makes sense.
Me, yes I look young and I am young to have a 5.5 year old, but I know I am an adult, I act like an adult, and I refuse to be treated as anything but. I'm married, I have two kids, I own my home, I own two cars, I pay all my own bills (on time), my house is always clean, I cook dinner every night, my DH works very hard and if necessary I work as well (not currently necessary) and as a result we do not depend on the system or anyone else for anything, I don't go out and party and leave my kids with other people, my kids are always taken care of and I feel like we are good parents and raise our kids to be good people, my kids and my responsibilities ALWAYS come first. I refuse to be seen or treated as anything but an adult, because I know that I am one in every way. If anyone sees me as needing to be treated as young or irresponsible, I am honestly unaware of it.