If the division between the top juniors and the top seniors is strictly by age, then each age group compete under pretty much the same rules, with opportunities to rack up points through jump difficulty, jump quality, difficult spins and steps, and all the program components.
Jump difficulty may be highest among the more athletic top juniors, but that doesn't mean that every elite junior medalist will be jumping the most difficult jumps, nor that every senior medalist will be watering down jump content or restricted to only lower content. The teens are allowed to rack up enough points to win through quality, and the 20-somethings are allowed to rack up enough points to win through difficulty, as well as vice versa.
Excellent skaters and performers with good jumps can win in both age categories, and excellent jumpers with good skating and performance quality can win in both age categories. Who wins any given event will depend who showed up and had a good skate that day.
Alternatively, if you want divisions by program type, then allow for plenty of age overlap with no maximum age in either event, make the rules significantly different, and call them by different names based on emphasis rather than the likely ages of the winners.