Hi Greg--
Yes, I have been to both Italy and Spain. In 2018 we spent 3 weeks in Florence, where we rented an apartment in a local neighborhood within walking distance of the main sites, it was part of a 3 month trip in Italy. We were never bored and saw the best of what Florence has to offer. We happened to be there on Easter and saw the festivities. I've been back to Italy 2 other times.
Spain; Barcelona, Valencia, Andalusia area, Marbella, Madrid, and Segovia. Also spent time in the Basque Region: Hondarribia, Guernica, and San Sebastián.
As far as being a slow walker, if you can get up and down stairs (in some places), but Florence is fairly flat, and over cobblestones, you should be fine in Florence.
Spain is varied as far as walking; some towns are hilly.
I don't want to steer you away from what you want to see, but I just think that Finland wouldn't be my first choice for a first time in Europe.