I know 70 would be a bit of a challenge, but for my son-in-law's 40th a few years ago, I bought him 40 different, relatively small, useful and not so useful gifts which he loved. I wrapped them all separately and packed them all in a laundry basket.
Over a period of a few weeks, he wrote me 40 different Thank You letters in reply which I still have, as they were very witty, and worth keeping. Apart from things he could keep, I bought things like Yorkshire tea bags (as he's a proud Yorkshireman), jar of honey, which he loves, a tin of venison pate, which all went down well.
One suggestion your family member might like could be to drive round Brand's Hatch, or somewhere similar. My husband treated me to this for my 60th, and I had a whale of a time. They do off-road driving as well as the race track.
I wouldn't particularly recommend a balloon flight as the weather is unpredictable, and my brother-in law had to have 6 changes of date before the weather was suitable.
Whatever you choose, I'm sure they'll love it!