For once, Wikipedia hasn't kept up - giving Steig's d.o.b. as Sept 23 1942, but not giving a date for his death.
I was born in 1939 and he did seem youthful to me when I saw him in the Free Trade Hall, Manchester in 1969 with a package that included the Thad Jones/Mel Lewis Orchestra, Freddie Hubbard, Richard Williams and Richard Groove Holmes.