I'm 47. I got here a day at a time. There wasn't a single one of those days that I said "oh, hell, today is the day that I turned 'old!' " It just gradually happens. I still lift heavy, train hard, and do my best to keep up with the 25-30 year old Special Operators I often train with. They're tough and don't cut me any slack.
I think most guys will agree the toughest muscle to train is the one between your ears. Not only training your mind to know that you're the toughest sumbitch in the gym, but also training your mind to know that you don't know everything and that you should be constantly learning. You'll learn from people not as knowledgeable as you, people younger, older, etc.
As far as the best way to age strongly? Form. Get your form dialed in. Learn when you're too fatigued to lift properly and call it a day. Nothing is more annoying than getting tired, hurting yourself, and losing a lot of hard-earned gains while your body heals.
It's also never too early to wean yourself off of junk food if its part of your diet. Sure, have a burger, burrito, and a day where you eat every damn thing you can cram into your mouth from time to time. Just ensure it's not a habit and don't let it become one.
Like JoeGood & daddyzombie say: GPP & FIsh Oil
In short, get your form dialed in, GPP, push yourself but don't be stupid about it, and get your nutrition right.
There aren't many better feelings than being strong when strength is required and chicks dig muscle and I'm just kinda rambling now.
I wish that 25 years ago I'd been smart enough to ask your question and smart enough to listen.
Best of luck to you and remember one thing:
Regret for what we've done can be tempered with time. Regret for what we did not do is inconsolable.
In other words, if there's something you really want to do get out there give it your ALL before it passes you by.