Half marathons are excellent races. At 13.1 miles (or 21.1K), they are long enough to give you great satisfaction from completing one, but short enough that you can recover quickly after one. They are also a great stepping stone for runners who want to move up in distance but who aren’t yet ready to tackle the marathon. As for a triathlon, swimming, cycling, running starts with the understanding of what you'll be doing on the day of your race. So 10-13 week training would be a good way to get started on preparing to pass through that finish line having fun.