30 doesn't bother me so much, it's the years at the back end of the 5-6 year deal that you give a guy at 30. Assuming Greg remains fairly healthy, I think he'll remain effective for a few more years.
Driver peaked at 31, but he remained essentially just as effective up to 34, where he at first gradually declined, then quickly declined. Reggie Wayne is 34, and he has remained consistent other than the year he didn't have Manning or Luck throwing to him, which was the aberration year. Welker is 31 and not really showing signs of decline. Moss hit a wall at 32 and T.O. about 34-35. I don't think 30 is a major concern, but 33-34 is starting to enter the danger area.
So I think a lot of guaranteed money on a 6 year deal would be a very bad idea to give Jennings, which I'm sure is what he'll be going for. If he could be landed on a 3-4 year deal, that seems relatively safe to me.
Frankly, if you can comfortably make it work with the cap, 1 year/$10M isn't a bad deal to bring Jennings back. I'd prefer a tag and trade, though. Would be nice to land a 2nd round pick for someone we didn't even expect back anyway.
Something that isnt always obvious but around 30 the drops seem to increase. Welker I believe had a large amount last year, Driver too. TO I remember always having a large amount of them. Wayne I dont recall if he drops many or not.