The Verdict: Need More Info
The United States is one of Portugal's youth mobility partners, but the age limit for Americans is not published. Ask the Portuguese consulate covering your state what it is and whether you are within it.
Portugal's visa portal gives the age range for every other agreement, from 18 to 30 up to 18 to 35, but names the United States without one. Any figure we gave you would be a guess, and on this route the age limit is the whole question.
Everything else works as usual: up to twelve months, no extension, work alongside the visit rather than as its purpose, and age checked on the date you apply.