my 2c wrote:
1:18 is an excellent time for a 15-year old with only informal training. You should definitely run XC in the fall and track in the spring. Contact the XC coach before school's out if possible to see how summer training is structured - it might start in June, or it might start in August. Until then, keep doing what you're doing. Just don't get too greedy, and watch out for injuries.
You're probably in shape right now to break 5:00 in a mile, run around 10:30 for 3200, or be close to 17:00 in a 5K. In a large high school with a large and competitive distance program, those are solid JV times. In an average high school program, you'd be in the top 1-3 places on the varsity team. And you can expect to run significantly faster once you have some structured training behind you.
You're a complete idiot. He runs 1:18 and he is 15, so clearly aerobically underdeveloped... that's 13.1 sub 6's in a row. If he stepped on the track right now he'd be sub-4:30, maybe around 9:30 -5 and would be sub 16:30 in the 5k, just as a rust buster, and faster after a couple of races. OP, definitely do XC and track (don't do indoor - you don't need to race 9 months of the year. Train over the winter).
For perspective, I have run 4:39 recently and can barely string together 10 6:40's.
Good luck OP.