The game itself and the Pro scene I think goes hand in hand in my opinion. Pro players have a great deal promoting the game to the audience and the overall number of regular players help League itself grow.
Looking at the way the scene is for both pro scene and the just casual players I would say another year is certain but after 2017 I really doubt if League will be as popular at that time.
In the pro scene the biggest tournament of the year Worlds; NA has looked awful and shows no real signs of getting better so why would any NA viewer watch the NA LCS for a year just to see NA get destroyed and sent packing after 1-2 weeks ? It's a waste to watch something for close to a year and the payment is a 2 week vacation.
The game itself well while it's popular I don't think it will stay being popular in my opinion. In short sweet opinions; the game just isn't rewarding at any level. If you play League to just have fun and normal games that is 100% FINE; however most people play Ranked and honestly the ranked system sucks and out dated so less and less players are even playing ranked. Most league players that play ranked also watch the LCS so if more and more players aren't even playing ranked to see what works with "meta" picks do you think they will keep watching the LCS? I don't.
Age limits ? I don't know the age limit to be able to play in the Pro scene; I think it's 17 but whats the cut off age limit ?
Lets say the cut off age limit is 28; whats the point of a 28 or 29 year old to still want to play League because its fun ? They get to challenger and that is the limit to their hard work fun but with no real reward but just because it's fun ?
Like 80% of League players will never make it past Diamond and what else is there to do ? Troll? After a while just liking ignoring a bully or trolling it's gets boring and after a while you don't seem to care as much more and more until after a while you just stop playing the game.
Overall this game has another year for both professional and ever day gamers but after 2017 I really doubt if anyone will care as much about League and it will fade away. As the pro scene is really just Korean dominance year after year so watching 2013-? so watching the pro scene you're really just recording the same episode of a show and watching it over and over again knowing the ending. The ranked system is again outdated and won't ever seem to change 6 years and counting.
Just my own opinion.