I started on a Honda also many years ago. Now several decades later, I would suggest the advice to just go ahead to the Sportster, but with the caveat that you take real instruction with it. Not just a ride around the area with a riding friend. At an almost exactly same height and weight to me, I can tell you, you can handle it. Likely better than I as I am already on the downhill side of the curve age wise.

The sage advice I did get, well too late to save my nearly dead left leg, was to drive as though you are totally invisible. Assume they NEVER see you. Motorcycles are by definition a defensive sport.

 

I started out riding dirt bikes as a kid, and being able to ride dirt will make you a better street rider. My first street bike was a chopped panhead (long time ago) that I still have. I learned on rear-brake only, suicide clutch fun. If you are careful and you have some experience (sounds like you do), you should not have any problems with the Sportster. 01dyna raises a good point, that being a lot of folks start on a non-Harley in order to minimize the risk of damaging and expensive bike. A lot of those folks don't have some experience to fall back on. Do yourself a favor and take a riding course. I did after 15 years of riding without a license, and I learned quite a bit. That too will make you a better rider.

When I was thinking about buying my first bike, I was looking at Triumph choppers and stuff, but I really wanted a Harley. A guy I worked with, older and with more experience, he told me to get the Harley. I would never be happy with anything else. I think he was right.

 

Usually I advice to start with 125-250cc. But as you have a dirtbike experience, feel free to buy a Sportster. Dirt riding gives much experience. Also Sportsters despite of 1200cc are unexpectedly plush if you are careful with throttle.

 

Take the training and get your license. But before you purchase a Sporty, rent one. There's an Eagle Rider not far from you: https://www.eaglerider.com/rentals

 

No, I've been told this by a lot of Harley owners. For reasons one person listed above like having something a bit cheaper is better to learn in case you drop it and bang it up in the process.

 

If you want a Sportster you're not going to be happy with a Honda. Worried about dropping a bike, buy a used Sporty and add crash bars. The used sportsters are very reasonably priced. But again, I suggest you take the opportunity to rent before you purchase. If you live in Brea you have an Eagle Rider close by that has a variety of bikes you can rent including Sportsters.

 

The Yamaha Bolt might be a good bike too. The bolt, the shadow, and the Iron 883 are all pretty similar in price too. If you're trying to save money now and upgrading later, you might just get the iron now since they are basically the same price anyways.
However, if you're wanting a 1200 then you might wait because there is a pretty substantial price increase.

 

Sounds about like my background.......after the dirt bikes and a scrambler I got a Norton 850 Commando. Very comparable to a Sportster of the era except faster. I'd say get the Sportster, 883 or 1200 is your only decision. As far as taking a course if you haven't ridden in years a "refresher" might be a good idea.

 

I started out on a 650cc sportbike, and within 2 months got rid of it for a 950cc sportbike. With someone your size, you shouldn't have any problems handling an 883 or even a 1200 Sportster.

 

a big +1 on renting a Sportster before buying, they are not right for everyone...could be you end up preferring sport bikes, adventure bikes, etc. down the line.
There is also the 883 vs. 1200 question, I rented one of each for a full day and decided I liked the 1200 much better. On paper Sportsters don't look like a great bet as they are overweight and underpowered compared to some of the competition but that is hardly surprising considering the basic design goes way back to 1957.
In practice I love mine, it has a LOT of character like the vintage British bikes I've owned without any of the headaches and plenty of power with a Stage 1 1200...plus lots of dealers that actually stock parts, a huge aftermarket, highly reliable and very easy to do DIY maintenance, etc.