The main problem with self-teaching from videos isn't your age, but that you can't see your own mistakes. On screen a parkour athlete looks smooth and effortless, but you can't assess their jump trajectory, center of gravity, or how they absorb impact on landing - none of that. That's where the danger lies: you'll repeat the movement thinking you're doing it right, but small deviations will pile up and lead to injury.
Find a class or at least a coach for a few sessions. Ask at sports clubs, check social media for local parkour communities - most cities have groups where enthusiasts train, and they'll help with advice or find you a good instructor. Even if you plan to train on your own later, it's better to work on the fundamentals first under supervision - landing technique, jumps from different heights, balancing on obstacles. It'll take a few weeks, but it'll save you months recovering from injuries.
At 25 your body does recover slower than it did at 18, but that's not a barrier - you just need to be more careful with training and not rush into jumping off tall structures. Start with low obstacles and basic stretching.