I don't know specifically about the soft parts in these boosters, but many manufacturers do have a recommended shelf life for elastomers or parts containing elastomers. I know some of the industrial manufacturers we represent at work have that lifespan set at 5 years +/-. Would this booster be OK? Probably just fine. I know my 35 year old booster was still working fine last year...I only replaced it because it was rusted to pieces externally. (I went with a reman unit from a local auto supply).
1994 F150 4x2 Flareside. 5.0 w/MAF, 4R70W, stock.
1984 F150 4X2 Flareside. Mild 302 w/ 5spd. Sold.
1980 F150 4X4 Flareside. 300i6 w/ 5spd. Sold in 2021.
1980 F100 4X2 Flareside. 351w/2bbl w/NP435. Sold in 1995