If you are just starting to get into road biking, the best use of your time is to be on your bike. The physiological changes necessary for good aerobic performance take time. Years, really. You have time to investigate all this. IMO, once you have the bike riding part down you can start looking for the smaller incremental gains which may or may not be possible from weight training, depending on how or if you want to specialize on the bike. Weight loss comes from riding lots and not replacing all the burned calories with food. IOW, discipline.

So for now, just go out and ride. When I was your age, I'd do 20-30 miles every day in hilly terrain. Explore your area and roads. When you see a hill, ride up it. Never walk, make it a matter of pride. Gradually increase the length of your rides. Do one longer ride every weekend. OTOH, don't be bummed if you can't ride like I did. I rode since I was 6. OTOH, pat yourself on the back if you can. Maybe you have talent.