What brand of tires are they?

Do the sidewalls or tread looked cracked?

The best thing to do is have one looked at by a pro. There are a lot of factors involved in how long they will last. (temp, humidity, age, wear, quality of the tire, etc)

__________________
You have your way. I have my way. As for the right way, the correct way, and the only way, it does not exist.

There is a rule of thumb in the industry that you can go 6 years from the date of manufacture. There is not a lot of agreement on the specifics of that rule of thumb. Some people worry about it when they buy tires and find out they have been in inventory for 2+ years. If I was going to use the tires up within the six years it wouldn't bother me personally.

The full answer depends greatly on the oxidation of the tire, usually the sidewall, so if it has been in the sun in California or Florida 6 years may be too long, and if they are stored properly in a cool dry place then they would be in much better shape.

Another factor for your friend is that tires have improved significantly over the past decade. A ten year old design is not going to perform like a modern tire, whether or not it is in as-built condition.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue

some other factors..., staggered set vs all 4 identical; what type of driving, hwy vs commute; how often is the tire air pressure checked; do you have proper wheel alignment - all can affect tread wear

__________________
Mark _______________________________
2001 X5 4.4i topaz blue/sand Sport, complete Dinan S2 , hitch, V1, tint, BSW Stage 1, Alpine INA-W910BT
___________
Life is not fair!
You can't protect people from their own stupidity!
Laughter makes life worth living

I interpreted it as an age question, not a mileage question, given the assumption that there was sufficient tread.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue

That's true, it's simply an age question.

And JCL is absolutely right about the weather and exposure of the tires. I had to replace tires on a BMW convertible about 6 or 7 years ago--they were just 5 years old, but had turned brittle after too much sun in CA.

I am not sure of the brand of the rubber but will look into it. The car in question is an ML320. Let me put it another way. Would you replace Diamaris after 6 years and 25,000 miles if there was more tread left?

__________________
-----

-'13 E93 M3 Cab, Interlagos Blue, Carbon Black leather, DCT, all options, and fun, endless fun!
-'13 X5 35i M-Sport, Carbon Black & Cinnamon, Dinan Stage 2!
-'15 Toyota Sienna Limited Premium AWD, Silver & Grey, Nav & BluRay, and less lame than the 2011 it replaced
-'07 Mini Cab S, Laser Blue, 6sp, endless fun that ended (sold)
-'04 X5 4.4i, loaded, loved, modded and sold

some manufacturers say 10 years for tyres but as was said , it depends on opperating conditions.
I usually bin tyres when the sidewall shows signs of crazing , that is like dried and cracked mud on a miniscule scale .
my experience of michelins` is that they craze sooner than most .
there is advice on storing tyres on some retailers websites .

just saw a '53 chevy with original tires and only 433 miles of the odometer on the Yahoo webpage - I wonder if the mileage was limited due to the flatspots

__________________
Mark _______________________________
2001 X5 4.4i topaz blue/sand Sport, complete Dinan S2 , hitch, V1, tint, BSW Stage 1, Alpine INA-W910BT
___________
Life is not fair!
You can't protect people from their own stupidity!
Laughter makes life worth living

I have read that racing teams stock up on tires when they are cheap and just store them properly until they are needed. apparently, they can't find a difference in performance after a couple years of storage...

In addition to the info above - I found the following (part 1 & 2) from TireRack to have some more details of interest.