Yay! Happy for you. ?
The age thing will be less and less as the two of you grow older.
As for the other part, I echo several others: Be happy, be yourself, tell her what you love about her and, without belaboring the point, let her know you are feeling some insecurity, still getting to know your own body on hormones, and appreciate her open-minded patience.

I’m dating someone 11 years younger, so I hear ya on that score. How exciting that you can explore and learn together what feels good and what feels better. Maintain open and honest conversation because if your body is still getting used to the hormones, your arousal and response may change over time.
Best wishes for an amazing second date!

Starting any new relationship is stressful. The best thing you can do is be yourself, stress to the other person that you are anxious and just need you both to take your time and communicate about anything that happens as you get to know each other. Communication is key. You will do fine.

First of all, congrats! Secondly, don't worry. You got this. She obviously likes you and since you're both trans, she will understand what you are going through with the hormones. Maybe go slow until you are more comfortable in/with your own body. Also, as with any relationship, communication is key. Just be yourself (after all, that's who she likes!), and try not to work yourself up. You'll do great!