Sydney will be fine - their over 30s are not essential for their structures.
Fremantle's over 30s are almost all structurally important (Pav, Sandilands, McPharlin).
Hawthorn's is a massive core of midfield talent with some structurally important players (Hale & Lake)
Geelong are in a similar boat to Hawthorn. (although I only count 7)
We have 7 now. We'll have 9 by next year (Stokes and Rivers), provided there are no retirements this year, which seems to be the case.