There are nice sonatinas from the Romantic Era (Spindler, Lynes, Lichner, Gurlitt, Biehl), but it's really difficult to find easier sonatas from that period.

I've seen Schumann's Sonata for the Young, but it's not too interesting. Grieg's Sonata in A minor has a nice first movement.

Sonatas by Liszt, Brahms, Chopin, Rachmaninoff, MacDowell, Weber, Schubert, and late Beethoven are too difficult (and too long). Any suggestions for easier sonatas from the Romantic Era?

Look at the Fanny Mendelssohn-Hensel Sonata in G Minor. It's not easy but I think it's certainly one of the easier ones. And maybe even Scharwenka.