Hey, it's absolutely (!!!) possible to have a healthy baby, as many of us have done. But, I think it's important to know going in that you'll probably be doing 10x more work than a Mom w/o T1. But, for me, it's sooo worth it to a) have my beautiful son and b) know I could have a baby after 26 years of living w/ T1. But, as soon as I knew I was pregnant, I worked out a deal with my boss about leave because by the end I had about 4 appts a week. I also needed to take short breaks to test my BG, correct, etc every 30-60 min during the work day.
As for age, it really depends on who you ask. I'm 33 and want another, but it's not a great time in my life, so I recently asked a few of my doctors about "age limits" for T1 Moms. One endo told me, not after 35 because then there's a double high-risk situation, whereas another endo told me I was healthy w/o complications (knock on wood!), so he was okay with me waiting until 35/36. A high risk OB I saw explained that there's a gradual increase in risk as you get older, so it's not like there's some magic cut-off that happens when you turn 35. So, younger is better, but there's no exact cut-off time for him.
In "real life" I know of a few T1 Mom's who have had babies in the 37-39 year old range.
I know you're not married yet. If you did decide to "do it alone" I'd make sure you have lots of support in your life b/c it's a lot of work.