You're not required to have a mechanical unless you want one or have extenuating circumstances, usually. The choice is well-debated throughout the forums.
Cardiologists will usually say mechanical just based on your age. Make sure that you are getting what suits you best. You have to live with it, not them, and the long-term survival odds (including the resurgery) are equivalent.
As far as how far along you are towards replacement... You don't want to wait until there is actual, permanent damage. One thing you can do about the heart size is check your oldest echoes through now. My LV went from the smallest normal size to the largest, then one knotch more. Then it was listed as "slight" or "mild." However, they rarely take into account the fact that it travelled all the way through the "normal" range first, which means it was quite enlarged, in comparison to itself. See if that's the case with you, if you have old enough echoes.
You're exhibiting symptoms, and that's a sign that you're getting close. Especially with regurgitation, the valve is frequently very calcified and inflexible, which usually doesn't seem to go into the cardiologists considerations. I have to wonder what some of your echo stats are.
Also, you have some risk of little pieces of calcium breaking off.
Exercise now will not help your heart, and may increase the enlargement. If there are things that definitely give you SOB or angina, stop doing them as much as is reasonable. This is not a good time to "shake it off" and move forward. Those symptoms mean your heart is struggling.
You can't fix your valve with force of will, but you can increase the damage to the rest of your heart. It isn't a manliness thing - we all wanted to try to ignore it, but it's not the best approach. You should consider no carrying of heavy boxes, helping people with heavy furniture move, or snow shovelling.
Also, I believe that atheletic people will stress test well, even though they're in trouble. The problem is that the muscles in an atheletic body require less oxygen to function, and tend to hide the malfuction level of the heart. Everything on those tests is rigged toward the "average" person. If you're a runner, you won't display the stress as a less active person would. However, it's not because of your heart: it's because of your well-trained, oxygen-conserving leg muscles. Just my opinion.
We've had competetive bicycle riders get thrown into immediate surgery with .5 valves, as they didn't know anything was wrong. (Opinion-forming information.)
It sounds like you're close and should bring your information to some surgeons to look at. Find out how much they want to do, i.e., both valves?, repair one and replace one? Just the aortic? Then consider your options. In the end, the doctors advise when and what, but you decide.
Best wishes,