Hi all! I'm sorry if this first post is a bit long, I've discovered something weird about myself this week and I'm looking for some advice or pointers from anyone who has been in a similar situation!
I started running (having done no formal cardio exercise before in my life almost literally ever) in May with Couch25K but found it quite easy so cheated (quite a lot) and graduated in about 3 weeks. Since then I've been running 5k about 3 or 4 times a week. I have never tried to go further and hadn't really noticed these runs getting any easier although I figured my speed must have been increasing and when I timed myself it seemed like there had been some improvement.
Anyway, this week I decided it was time to try and run a bit further to see what it was like. I set off at a slower pace than usual with the intention of doing an extra couple of k. I thought this would be a struggle but doable with a bit of a push. Well, very surprisingly, I found it incredibly easy and ended up running for 13k with absolutely no problems at all. I felt like I could have kept on going forever and ever basically. I thought it might catch up with me the day after but I didn't ache at all so I decided to see if it was replicable. After one rest day I went out again yesterday and easily managed 16k. 10 miles! How is this possible? I really didn't even think I was any good at running, I'm used to feeling like my 5k runs are exhausting. My pace wasn't bad either- 13k in 76 mins and 16k in 95 so it wasn't as if I was just walking it.
After that (slightly lengthy) post my actual questions are: is this vaguely normal? Is it really risky to run like this with no build up? And how soon do you think it's sensible to attempt a half marathon? (I feel like I could run that distance now but I'm guessing it wouldn't be wise?)
For context, I am small and quite young so I imagine at a natural advantage. I'm clueless about serious running though so need guidance!
Thanks for reading. Any and all advice will be very appreciated 
(Also sorry if this all sounds a bit braggy, my intention is not just to show off my new found running super power )