Personality development?

When I was young, most things were enjoyable even if I put very little effort into them. As I got older, I realized the most rewarding activities were the ones I happened to put a lot of effort into over a long period of time.

For example:
- I ran 5-10k races in high school, and it was always OK, but as I got older I got better at it and it became more rewarding.
- I really loved movies when I was younger, and I still do but my enjoyment hasn't increased because I never put effort into it.
- I've always been into math and Excel, and this encouraged me to put effort into using excel for personal projects as I was younger. Now, this spreadsheet skill is a pillar of my career and something fun I can do for friends on their random projects.

I hope you see the point I'm trying to make, because you are asking a really important question. Most people are trying to be the best person they can be. What generally causes a person to "grow up" is when they see the benefit of making investments in their own lives. Sometimes this is forced on them by circumstance, sometimes they discover this accidentally. Start making little investments in yourself every day and in a few years you will see what I mean.

Tiffanie!

This is such a perpetual process. A series of moments and realizations strung together. I hope you keep encountering these moments on your path through life.

Keep company that inspires you, and challenges you to become better in positive ways, for you and the world. This could take the form of classmates, family members, teachers, political figures on video. Take notes on the inspirations, and think about what actions you're inspired to do. Then - don't just think about it, make an action plan. There is a difference between thought, intent, and action. The gap can be just a small step to action in some situations, and in others it can feel like a large chasm.

Expose yourself to the news in areas or ways you care.
Write to projects that you're interested in, in order to get involved. They won't know unless you ask.
If you're driven to do something and don't see an initiative to jump onto, start one. Some of the time it seems harder than it actually is. Think through your approach. Ask yourself the hard questions - the ways a project might fail. Think it through.

There is a school of thought regarding effort and following your passions. Inspiration is part of this, but understanding which challenges you'll face (and if your commitment level lends you the fortitude to get through) is huge. This gentleman has some great writing on this topic - and won't beat around the bush.
Check it out:
https://markmanson.net/question

Regarding age and responsibility -
This is something people generally grow into over time, and assume as they are ready - but there is an age where you become legally accountable for what you do. Income, bills, housing responsibilities, renter's insurance, car insurance, paying taxes - this is all on you. There aren't as many easy, approachable resources as I'd like for learning about things like financial accountability, but it helps if you have someone savvy in your life that seems knowledgeable and willing to help guide you. Don't have someone around? Maybe ask a teacher, librarian, club leader - someone in your life who you think might be able to provide you with some framework to plan for saving and strategically getting ahead in your future.

I'm not sure if this is super helpful, but it's one of the better online resources I rolled across today. I recommend asking some people you look up to in your life for advice, but if that doesn't take you where you need to go, please take a look here.
http://www.cde.ca.gov/eo/in/fl/finlitk12.asp

Personality development is the relatively enduring pattern of thoughts, feelings, and behaviors that distinguish individuals from one another. The dominant view in the field of personality psychology today holds that personality emerges early and continues to change in meaningful ways throughout the lifespan. Evidence from large-scale, long-term studies has supported this perspective.