Yes, the Winter Soldier comic is considered canon within the Marvel Comics universe. It plays an important role in shaping the character's story and continuity.
The Winter Soldier's age in the comic varies depending on the specific storyline and continuity. But typically, he's depicted as being in his 30s or 40s.
The number of Marvel comic heroes is constantly changing and growing. As of now, there are well over 8000 characters, but new ones are always being introduced.