I would say that if you feel ready, go for it! We found out I got pregnant when my first son was just 6 1/2 mos old! Surprise! We were very excited even though we were surprised, and honestly the hardest part of it is that I didn't get much chance to enjoy fitting into all my normal clothes in between pregnancies. Oh well. My first and my second are just 15 mos appart, and I wont tell you that its all a breeze (I can barely remember my second's newborn days because I was so overtired and so busy running back and forth from one to the other all day long that its just a blur for the first 2-3 mos) there are things that are harder abot having them that close together, but there are other things that are just wonderful, that make it so that even though my second is only 6 mos old, I have already been thinking about when I want to have my third, LOL!
Some things that are hard are that the older one will still be very much dependant on your for everything, and will also be at the age where he is getting into ALOT more mischief. I can't tell you how many times I sat down to nurse my baby when I noticed that my toddler was about to fall down the stairs because I forgot to put a gate up, splashing in the toilet because I forgot to close the bathroom door, climbing on the table, or getting into a cabinet or the trash... LOL It's a learned skill to get up and run across the room with a baby attached to your boob! I feel kinda guilty because I never have too much time to just sit and enjoy my baby... that seems to only happen while my toddler is down for naps or already in bed for the night. Meanwhile, I would also feel guilty on days when my baby is so demanding (thankfully this was mostly in the first 6 weeks) that he had to be in my lap all day, and my toddler was having meltdowns because he wasnt getting any attention. Although, I think the last two things I just said probably happen regarless of what ages yoru children are. But, things were a bit more complicated as well because my older child could not talk yet to tell us what he wanted... he is better at it now but its still a work in progress.
So, yes, it can be hard because they are close in age, but it can also be easier in some ways too.
Ways that I have really enjoyed having two this close is that my older child has NEVER gotten jealous of his younger brother... yes, there was once or twice when he tried to push Ely out of my lap because he wanted my attention, but mostly, we have never had to deal with older sibling jealousy. He just LOVES his little brother and knew he was part of the family right away. We had to teach him what "gentle" meant when Ely first arrived, and yes, sometimes he hurts Ely without meaning too, but overall we were very surprised at how tough a tiny little newborn actually is! for the first three months, Gawyn smothered Ely in kisses and hugs and just loved him so much, and then finally Ely actually got old enough to start showing how much he ALSO adores Gawyn just as much... it is the MOST PRECIOUS thing to see them laughing at eachother and playing together. Gawyn can make Ely laugh out loud better than I can! Those are the moments when I just LOVE that I have two and not just one. And, it is so cute to see my older one get so concerned when his baby brother cries... he will run over and get his pacifier and put it in his mouth for me, get him a toy for me, and even put a blanket over him if I ask him too. Sometimes I am even able to get more done because Gawyn will go entertain his little brother for me when he is fussy and I am trying to finish dinner ect.
So, as I said, good and bad things about having them this close. I don't regret it, and I love that they have a sibling to play with. Gawyn will never remember life without a younger brother, so I hope that they always stay so close and continue getting along so well. Financially, two children isn't much more of a burden than one ($50 a month in diapers, none for formula since I breastfeed and Ely pretty much just wears hand-me-downs) My hubby and I are both students, it's still one more year til he graduates with his bachelors, and yes, things are TIGHT. I am a stay at home mom, and he works full time and goes to school full time to support our family. Sometimes we don't see too much of him, since he leaves before we get up and comes home after the kids are asleep a lot of nights, but we do it, and we are happy. I have noticed that having two kids is a little harder on our marriage than just one, and it think its just that there is less time you spend with eachother, since most of your time together is both of you running back and forth to whatever child needs something every few minutes. But, we make it work, and we are very happy, and I wouldn't change it for anything.
Good luck to you. We are pretty young as well, I'm 25 and hubby is 24. I just wanted to let you know that it can be done, and that there are positives and negatives to choosing to wait and to going forward with it!
***EDITED*** I just read a few of the other posts and wanted to mention a few other things:
I forgot to mention that one thing I do feel bad about with having two so close is that my first had to be weaned WAY before I or he was ready. My milk just dried up when I got pregnant again (it probably could have stopped it if I had know I was preggo and was eating better) but, by the time he was 9 mos he was fully weaned, and if I hadn't gotten pregnant I probably woudl have nursed him til he was over a year. We had some extra complications weaning him early because he was allergic to milk and we had to try to get him to have soy formula and drink soymilk instead of regular milk, which was PRICEY! He got really skinny durring the transistion from nursing to sippy cup because he wasn't getting enough food and he went from the 75th percentile in weight and height to the 20th in just 3 mos. thankfully once he figured out how to drink from the sippy he gained it back, but part of me wonders if his growth was stunted because of it. He is still tall for his age, but with my hubby being 6'5 I sometimes imagine that he would be taller than he is.
Also, a few of the other posters mentioned that you had asked some questions about marital trouble... I know I already mentioned that 2 kids is a lot harder than one on your marriage, but I just wanted to re-emphasize. My hubby and I have an awesome marriage and always have, but adding another child in the mix still made things harder for us while adjusting, and I can only imagine that it would have been a lot tougher than it was if our marriage wasn't stable to being with.
Also, I agree with what some moms are saying about toddler a lot more work than you are expecting. I think its totally doable, but I could not have imagined having another child when my first was between 10 and 14 mos old... they are very mobile but have NO SENSE of danger or even balance and you have to watch them like a HAWK! It's amazing they even make it through those months! Babies are really easy when they are young - they just eat, sleep and poop... It wasn't until my first got to be about 1 that I really started to feel like motherhood was really getting challenging.