I started triathlon in 2016 when I was 41 and have been hooked ever since. I had to learn how to swim from scratch pretty much and whilst I'm a decent cyclist my run was pretty poor. Over that time my training has progressed and I've entered longer and tougher events, I'll be doing my third half iron distance race this year in 2 weeks at Challenge Paguera. I've entered my first full Ironman (IM Wales) next year.
Whilst you can do all of this on your own I have found joining a club invaluable. You meet a lot of like minded and friendly people and you pick up so many tips from experienced members who all remember what it was like starting out. My main advice would be to join a local Tri club, you won't regret it. Also, keep chipping away at the things that you're weak on. For me it was my swimming and I can now comfortably swim 5k at a decent pace.