No single individual can actually observe all 613 mitzvot, not only because conditions might not allow it, but because there is no individual to whom they all apply.
Some mitzvot are commanded exclusively to women, others exclusively to men.
Some apply only to the king or the kohen gadol ("high priest"), whereas other people are actually forbidden to observe them.
But every Jew has some connection with each of the mitzvot, and, in a certain sense, can observe them all.
For example, the high priest or the king fulfills his mitzvot on his own behalf and on behalf of all Israel.
All of Israel in a particular generation, and in a broader sense of all generations, constitutes a 'komah sheleimah,' a singular unit, just as the human body, consisting of different limbs and organs, constitutes a single organism.
Israel, in this sense, is a multidimensional being, in time as well as space, its various generations and communities composing an integrated whole.
Each generation is a cross section of the greater body, personifying the totality in its specific way.
Each individual, therefore, as a part of the whole, shares in the mitzvot that every other part observes.
–Rabbi Adin Steinsaltz
From Opening the Tanya, p. 124, by Rabbi Adin Steinsaltz