I think pinsonp nailed it. Age doesn't have anything to do with absolute strength or speed or flexibility (though individuals will lose a little over the years, most of the 70 year olds I ride with can leave me in the dust, too) - but age DOES affect our ability to adapt to new things. This is something I saw over and over again as a disability claimants' advocate, and it's even part of the statutory structure of disability eligibility. Ability to adapt starts to decline around age 45! And even though just like physical fitness, we can slow the process quite a bit by staying mentally fit, it still happens to all of us at some point and at some rate.

That said ... it depends on how much you WANT to learn to ride a road bike. You can do it if you want, I know that for sure without even knowing you, but there are some things you really have to want to do. You're the only one who knows whether you want it that badly.

As far as triple vs compact, many bike shops will swap drivetrain components out for you on a new bike for free or for just the difference in cost. Check before buying, since this isn't universal, but it's kind of one of the things that will let you know how customer-oriented a bike shop is.