If it's bigger scale you want, and that means influencing decision making and policy, you need the knowledge to back your passion up. If being a local Councillor is appealing, you've missed the boat in the latest election BUT you can spend the next few years building up your knowledge and credibility so that you know what you are talking about and the impacts from decision making.
Ellen MacArthur foundation has courses that can help you decide how to focus your passion. These are either a few weeks long or just info slides. Once something strikes a chord, then look for building your knowledge. Volunteer with an organisation or see if you can start one up. Once your credibility is there you can run to be a councillor to make a difference.
As well as the ecology and environmental management route you could look at Urban Planning (or Town Planning) as this career option works with creating the policy that determines where new development is located and how it's impact on the environment is reduced and sustainability measures are included. Having some understanding if this area can help if you want to be a councillor but also f you choose to be an activist or community volunteer trying to improve your local environment.
It's all very well people dismissing small scale action or local action as being only a drop in the ocean, but the more that is being done to make the "least environmentally impactful" choice the easy one for people, the more likely they will do it and the knock on or ripple effect happens.
So help folk make the decision not to use their car - can you set up a business reclaiming bikes from the local tip/recycling centre, work with someone to refurb and then sell them or hire them out for local trips? A bike shop here hires out bikes and one is a cargo bike.
Set up a clothing exchange? Or Take in old clothes and fix or mend or repurpose then sell. Or use as rags for other purposes or work with a charity to see if one out there has a need or use?
If you like growing, can you volunteer to set up a gardening club at local schools and nurseries? They can grow flowers and vegetables and encourage biodiversity back in to developed spaces. Also care homes would be happy for this too as it can involve residents but also make nice spaces for them to enjoy.
These are small actions but worthwhile.