I think hes good for a few more films to come, guy looks good hes still got some good skin and excellent hair, he looks younger then some of my m8s that are in there late 20s even.
And thats why we have stunt doubles galore
Theres plenty of Avengers left and RDJ can always do the voicing for iron man and if anything every now and then his helmet can come down and we can either see his face or have a CGI fan underneath