I'll add my two-bits, too.

I'm 68 and I still backpack solo several times a year, so age isn't really the biggest factor that could stop you, it's gaining the knowledge and experience to guide you to having successful trips. It's obvious you have motivation and enthusiasm, and those are very valuable to get you started and keep you going. But motivation and enthusiasm can lead you into biting off more than you can chew, which can lead to discouragement or (heaven forbid) stress injuries.

It sounds like you're working on your conditioning the best way, by hiking! Being in good condition is extremely helpful. Keep at it!

Now, as they say in the late night TV ads,"But wait, there's more!" If you're going to backpack there's the overnight camping aspect to consider, too. A lot of us here who are backpacking into our 60s and 70s started out camping and hiking when we were young, so we forget how that base of knowledge and experience gave us a solid understanding of what to expect when we graduated to backpacking, and how we've been building on that knowledge for decades.

I'm not pointing this out to scare you off, only to underline that it's much better to add to your knowledge and experience by gradual steps. For example, if you haven't camped much before, take all the items you think you'd need to carry for a one-night trip and 'camp out' with them in your yard or at a campground to see how they work out. Try carrying the whole load out on a trail, but without staying overnight, just learning how the weight feels. In other words, test things in a low-risk situation first and build your way up to bigger challenges.

I think everyone who has answered so far would agree that backpacking has been a hugely beneficial part of our lives. We've seen things and learned things about the world and ourselves that are wonderful and humbling. That's why we want you to succeed in your biggest most ambitious plans. For us they're been well worth all the sweat and the mosquitoes. Probably for you, too.

Come back and ask questions. Someone will always try to answer them. Happy hiking!