It depends entirely on the person I believe. Personally, my 30's were indeed better but, that's because in my mid 20's, things got so bad, but I still had enough motivation/ energy/ hope/ will to make huge changes in my life to turn things around. And, for a while- while it was still one hell of a struggle, it worked. Or at least- it put me in a better position than in my 20's.
I think it very rarely happens by magic though. Mostly, I think the person needs enough impetus to be able to put in that effort to change. That's going to be much harder for some than others. Plus- sadly- it doesn't always work out. No matter how hard you try. My ideation never really went. It just got put into the background for a few years. Living became easier for a while because I had enough interest in the things that distracted me best.
It hasn't 'solved' the issue though. Ideation hit in strongly again when my said coping mechanism started to fail a few years back.
The whole 'it gets better' really pisses me off though. It's such a passive idea. Your fairy godmother shows up and grants all your wishes or something. Maybe some people's lives work like that but, I don't know many who's have. Those people I know who have successful careers, loving relationships, amazing hobbies, active social lives- they went out and got those things and they work hard constantly to maintain them. It ought to be: Things might get better- so long as you put in huge amounts of effort to try to make them better. When someone's suicidally depressed, it's not exactly probable that they'll have the energy for all that.